Fix warning about unsafe flag operation in qqmltypecompiler.cpp.

compiler\qqmltypecompiler.cpp:1192: warning: C4806: '&' : unsafe operation: no value of type 'bool' promoted to type 'QQmlCustomParser::Flag' can equal the given constant

Change-Id: I2bc4add832a4382529d63de892e37c17f2670c4a
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>