Fix crash when using down cursor in an empty math subscript (Bug 4117).

http://bugzilla.lyx.org/show_bug.cgi?id=4117 

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/branches/BRANCH_1_5_X@19689 a592a061-630c-0410-9148-cb99ea01b6c8

src/Cursor.cpp

@@ -1482,12 +1482,14 @@ Font Cursor::getFont() const
 }
 
 
-void Cursor::fixIfBroken()
+bool Cursor::fixIfBroken()
 {
 	if (DocIterator::fixIfBroken()) {
 			clearSelection();
 			resetAnchor();
+			return true;
 	}
+	return false;
 }
 
 

src/Cursor.h

@@ -179,8 +179,9 @@ public:
 	 * Not using noUpdate() should never be wrong.
 	 */
 	void noUpdate();
-	/// fix cursor in circumstances that should never happen
-	void fixIfBroken();
+	/// fix cursor in circumstances that should never happen.
+	/// \retval true if a fix occured.
+	bool fixIfBroken();
 
 	/// output
 	friend std::ostream & operator<<(std::ostream & os, Cursor const & cur);

src/mathed/InsetMathNest.cpp

@@ -568,7 +568,15 @@ goto_char_backwards:
 			// notify left insets and give them chance to set update flags
 			lyx::notifyCursorLeaves(cur.beforeDispatchCursor(), cur);
 			cur.fixIfBroken();
-		}	else
+			break;
+		}
+		
+		if (cur.fixIfBroken())
+			// FIXME: Something bad happened. We pass the corrected Cursor
+			// instead of letting things go worse.
+			break;
+
+		// We did not manage to move the cursor.
 		cur.undispatched();
 		break;
 	}

status.15x

@@ -76,6 +76,8 @@ What's new
 - Fix crash when a user removes a formula when its preview is being generated.
   (gcc 3 only).
 
+- Fix crash when using down cursor in an empty math subscript (Bug 4117).
+
 * DOCUMENTATION
 
 - Embedded Objects manual: section about longtable alignment added