Be less verbose about invalid keysyms

Report invalid keysyms only when DEBUG_GENERATOR is defined.

It is not unusal that Qt applications are used on old linux
distributions where Compose files might be far behind the current
development, therefore we should be less verbose when encountering
invalid keysyms. On Red Hat 5 compose key plugin reports ~3200 lines of
warning messages:

"Qt Warning - invalid keysym: U1001D1BC"
"Qt Warning - invalid keysym: U1001D16F"
"Qt Warning - invalid keysym: U1001D1BA"
"Qt Warning - invalid keysym: U1001D165"
"Qt Warning - invalid keysym: U1001D16F"
...

Task-number: QTBUG-34483

Change-Id: If0c51d300508ef164ad7fc59b0a76a838cd5a3b9
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

src/plugins/platforminputcontexts/compose/generator/qtablegenerator.cpp

@@ -430,8 +430,10 @@ void TableGenerator::parseKeySequence(char *line)
                     elem.keys[i] = XKB_KEY_dead_invertedbreve;
                 else if (!strcmp(sym, "dead_double_grave"))
                     elem.keys[i] = XKB_KEY_dead_doublegrave;
+#ifdef DEBUG_GENERATOR
                 else
                     qWarning() << QString("Qt Warning - invalid keysym: %1").arg(sym);
+#endif
             }
         } else {
             elem.keys[i] = 0;