Because of C++'s operator precedence, '!' logically negated all_event_masks only instead of the whole expression.
This resulted in the condition always being false and XTest never being used.

Adding a pair of brackets fixes it.

BUG: 362941
BUG: 375017

Verifed with debug output that XTest is being used when XCB_EVENT_MASK_BUTTON_PRESS is not set in all_event_masks.

Tested with a couple of applications:

• mplayerc.exe: wine app, worked before, no XTest, still works
• tvbrowser, jedit, jitsi 2.8: java apps, didn't work before, use XTest now and work
• ksensors, ksteak, kconnections, klinpopup, ktvschedule: KDE3 apps, worked before, no XTest, still work
• wammu: python/wxWidgets app, worked before, no XTest, still works
• grip, avidemux2, hexchat: gtk2 apps, worked before, no XTest, still work
• audacious, stardict: gtk3 apps, didn't work before (unless GDK_CORE_DEVICE_EVENTS=1 was set), work now using XTest (without GDK_CORE_DEVICE_EVENTS=1)