Improvement of Improve error reporting with buggy custom G-code sections #1516

Errors in the file output templates are reported in mono-spaced font,
so that the arrow character ^ is displayed at the right column
pointing to the offending spot.

src/libslic3r/GCode.cpp

@@ -756,7 +756,7 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessor::Result* re
         msg += "        !!!!! Failed to process the custom G-code template ...\n";
         msg += "and\n";
         msg += "        !!!!! End of an error report for the custom G-code template ...\n";
-        throw Slic3r::RuntimeError(msg);
+        throw Slic3r::PlaceholderParserError(msg);
     }
 
     BOOST_LOG_TRIVIAL(debug) << "Start processing gcode, " << log_memory_info();