Test error name is non-empty for the whole range

tinyxml2.cpp

@@ -1964,7 +1964,9 @@ void XMLDocument::SetError( XMLError error, const char* str1, const char* str2 )
 const char* XMLDocument::ErrorName() const
 {
 	TIXMLASSERT( _errorID >= 0 && _errorID < XML_ERROR_COUNT );
-	return _errorNames[_errorID];
+    const char* errorName = _errorNames[_errorID];
+    TIXMLASSERT( errorName && errorName[0] );
+    return errorName;
 }
 
 void XMLDocument::PrintError() const

xmltest.cpp

@@ -1498,6 +1498,14 @@ int main( int argc, const char ** argv )
 	    delete doc;
     }
 
+	{
+		XMLDocument doc;
+		for( int i = 0; i < XML_ERROR_COUNT; i++ ) {
+			doc.SetError( (XMLError)i, 0, 0 );
+			doc.ErrorName();
+		}
+	}
+
     // ----------- Performance tracking --------------
 	{
 #if defined( _MSC_VER )