coverity#736100 Improper use of negative value

Change-Id: Ia5cf36b64841f2d465c922da40008a540cc6caf7

starmath/source/cursor.cxx

@@ -933,7 +933,9 @@ void SmCursor::InsertFraction() {
     //Find Parent and offset in parent
     SmStructureNode *pLineParent = pLine->GetParent();
     int nParentIndex = pLineParent->IndexOfSubNode(pLine);
-    OSL_ENSURE(nParentIndex != -1, "pLine must be a subnode of pLineParent!");
+    assert(nParentIndex != -1); //pLine must be a subnode of pLineParent!
+    if (nParentIndex == -1)
+        return;
 
     //We begin modifying the tree here
     BeginEdit();