UI: Set browser hwaccel def. to false if winver <=7

Due to reports of issues with Windows 7, if the user is on windows
version 7 or below, set the default for "Browser Source Hardware
Acceleration" to false instead of true.  This ensures optimal user
experience and still allows those who had it working to continue using
it if they so choose.

Exact cause for this issue on Windows 7 is currently unknown.

UI/obs-app.cpp

@@ -435,9 +435,12 @@ bool OBSApp::InitGlobalConfigDefaults()
 			"MultiviewDrawAreas", true);
 
 #ifdef _WIN32
+	uint32_t winver = GetWindowsVersion();
+
 	config_set_default_bool(globalConfig, "Audio", "DisableAudioDucking",
 			true);
-	config_set_default_bool(globalConfig, "General", "BrowserHWAccel", true);
+	config_set_default_bool(globalConfig, "General", "BrowserHWAccel",
+			winver > 0x601);
 #endif
 
 #ifdef __APPLE__