Fix wrong parse of macro parameter and crash

Copy-pasting $#\n$ from text to LyX gives the error message:

    MathMacroArgument::MathMacroArgument: wrong Argument id

and it is not hard to get a crash soon after.

There are legitimate uses of # not followed by 1..9 in LaTeX and it is good to
parse them correctly when importing from LaTeX.

src/mathed/MathMacroArgument.cpp

@@ -16,15 +16,49 @@
 #include "MathSupport.h"
 
 #include "support/debug.h"
+#include "support/lassert.h"
 
 
 namespace lyx {
 
+
+Inset * InsetMathHash::clone() const
+{
+	return new InsetMathHash(*this);
+}
+
+
+void InsetMathHash::write(WriteStream & os) const
+{
+	os << str_;
+}
+
+
+void InsetMathHash::metrics(MetricsInfo & mi, Dimension & dim) const
+{
+	metricsStrRedBlack(mi, dim, str_);
+}
+
+
+void InsetMathHash::draw(PainterInfo & pi, int x, int y) const
+{
+	drawStrRed(pi, x, y, str_);
+}
+
+
+void InsetMathHash::normalize(NormalStream & os) const
+{
+	os << "[hash " << str_ << "] ";
+}
+
+
 MathMacroArgument::MathMacroArgument(int n)
 	: number_(n)
 {
 	if (n < 1 || n > 9) {
-		LYXERR0("MathMacroArgument::MathMacroArgument: wrong Argument id: " << n);
+		LYXERR0("MathMacroArgument::MathMacroArgument: wrong Argument id: "
+		        << n);
+		LASSERT(false, n = 1);
 	}
 
 	// The profiler tells us not to use
@@ -32,7 +66,6 @@ MathMacroArgument::MathMacroArgument(int n)
 	// so we do the conversion of n to ASCII manually.
 	// This works because 1 <= n <= 9.
 	str_.resize(2);
-	str_[0] = '#';
 	str_[1] = '0' + n;
 }
 
@@ -47,6 +80,7 @@ void MathMacroArgument::setNumber(int n)
 {
 	if (n < 1 || n > 9) {
 		LYXERR0("MathMacroArgument::setNumber: wrong Argument id: " << n);
+		LASSERT(false, return);
 	}
 
 	number_ = n;
@@ -54,24 +88,6 @@ void MathMacroArgument::setNumber(int n)
 }
 
 
-void MathMacroArgument::write(WriteStream & os) const
-{
-	os << str_;
-}
-
-
-void MathMacroArgument::metrics(MetricsInfo & mi, Dimension & dim) const
-{
-	metricsStrRedBlack(mi, dim, str_);
-}
-
-
-void MathMacroArgument::draw(PainterInfo & pi, int x, int y) const
-{
-	drawStrRed(pi, x, y, str_);
-}
-
-
 void MathMacroArgument::normalize(NormalStream & os) const
 {
 	os << "[macroarg " << str_ << "] ";

src/mathed/MathMacroArgument.h

@@ -21,22 +21,14 @@
 namespace lyx {
 
 
-/// A macro argument.
-class MathMacroArgument : public InsetMath {
+// A # that failed to parse
+class InsetMathHash : public InsetMath {
 public:
-	///
-	explicit MathMacroArgument(int number);
+	InsetMathHash(docstring const & str = docstring()) : str_('#' + str) {};
 	///
 	void metrics(MetricsInfo & mi, Dimension & dim) const;
 	///
 	void draw(PainterInfo &, int x, int y) const;
-	///
-	int number() const { return number_; }
-	///
-	void setNumber(int n);
-	///
-	InsetCode lyxCode() const { return MATH_MACROARG_CODE; }
-
 	///
 	void normalize(NormalStream &) const;
 	///
@@ -44,13 +36,35 @@ public:
 
 private:
 	Inset * clone() const;
-	/// A number between 1 and 9
-	int number_;
+
+protected:
 	///
 	docstring str_;
 };
 
 
+/// A macro argument.
+class MathMacroArgument : public InsetMathHash {
+public:
+	/// Assumes 0 < number <= 9
+	explicit MathMacroArgument(int number);
+	///
+	int number() const { return number_; }
+	/// Assumes 0 < n <= 9
+	void setNumber(int n);
+	///
+	InsetCode lyxCode() const { return MATH_MACROARG_CODE; }
+
+	///
+	void normalize(NormalStream &) const;
+
+private:
+	Inset * clone() const;
+	/// A number between 1 and 9
+	int number_;
+};
+
+
 } // namespace lyx
 
 #endif

src/mathed/MathParser.cpp

@@ -929,9 +929,13 @@ bool Parser::parse1(InsetMathGrid & grid, unsigned flags,
 		}
 
 		else if (t.cat() == catParameter) {
-			Token const & n	= getToken();
-			if (n.character())
-				cell->push_back(MathAtom(new MathMacroArgument(n.character()-'0')));
+			Token const & n	= nextToken();
+			char_type c = n.character();
+			if (c && '0' < c && c <= '9') {
+				cell->push_back(MathAtom(new MathMacroArgument(c - '0')));
+				getToken();
+			} else
+				cell->push_back(MathAtom(new InsetMathHash()));
 		}
 
 		else if (t.cat() == catActive)