Do not crash with empty (invalid) math environments (part of #8359)

src/mathed/MathParser.cpp

@@ -1478,6 +1478,13 @@ bool Parser::parse1(InsetMathGrid & grid, unsigned flags,
 
 		else if (t.cs() == "begin") {
 			docstring const name = getArg('{', '}');
+			
+			if (name.empty()) {
+				success_ = false;
+				error("found invalid environment");
+				return success_;
+			}
+			
 			environments_.push_back(name);
 
 			if (name == "array" || name == "subarray") {

status.20x

@@ -52,6 +52,9 @@ What's new
 
 * DOCUMENT INPUT/OUTPUT
 
+- Do not crash when loading documents with empty (invalid) math environments
+  (part of bug 8359).
+
 - Rerun makeindex if all nomencl entries have been removed (bug 8905).
 
 
@@ -66,6 +69,9 @@ What's new
 
 - Fix crash when optional argument inside a math macro was deleted (bug 8329).
 
+- Fix math-ams-matrix function that could corrupt documents if not used properly
+  (part of bug 8359).
+
 - Fix problem that led to assertion in some cases when space was at
   beginning of line (bugs 8838 and 8947).