Speed up compose file parsing in the X11 composition input method plugin

There's no need to decode the string until the end of the line, it's
sufficient to stop at the end of the quotes.

Change-Id: Ie617d2538511e91d0e0146f98b7e5ea3213b8db2
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

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

@@ -399,7 +399,7 @@ void TableGenerator::parseKeySequence(char *line)
         // handle direct text encoded in the locale
         if (*composeValue == '\\')
             ++composeValue;
-        elem.value = QString::fromLocal8Bit(composeValue).at(0).unicode();
+        elem.value = QString::fromLocal8Bit(composeValue, composeValueEnd - composeValue).at(0).unicode();
         ++composeValue;
     }