Fix bug #8089: Handle spaces at the end of the stream

If the stream is good (i.e. there are still tokens) and we expect an
argument, we call getArg(). However, if there are only spaces, the stream
suddenly isn't good anymore after 'skipSpaces' and we would get an error
when calling 'getChar'. Therefore we have to check whether the stream is
still good.

MathParser: Do not rewind the stream if we can't read from it

If the stream is not good, we don't need to 'putback', because we didn't
read anything yet. If we now do rewind the stream, we are asking for
problems as in bug #8089.

This was introduced in [3cafb856\lyxgit] to fix bug #4318.

(cherry picked from commit 26dcfcd343)
(cherry picked from commit 1ef930c058)

src/mathed/MathParser.cpp

@@ -535,7 +535,6 @@ char_type Parser::getChar()
 {
 	if (!good()) {
 		error("The input stream is not well...");
-		putback();
 		return 0;
 	}
 	return tokens_[pos_++].character();
@@ -544,9 +543,12 @@ char_type Parser::getChar()
 
 docstring Parser::getArg(char_type left, char_type right)
 {
+	docstring result;
 	skipSpaces();
 
-	docstring result;
+	if (!good())
+		return result;
+
 	char_type c = getChar();
 
 	if (c != left)

status.20x

@@ -103,6 +103,8 @@ What's new
 
 - Fixed assertion on selection of insets in RTL text (bug 7518).
 
+- Fixed an infinite loop when pasting '\\ ' into math (bug 8089).
+
 - Don't reset the selected format each time we click into a new paragraph
   in View->Source (bug 7997).