In x11, windows and osx crash handlers, check project settings exists
before looking up the crash handler message setting.
Avoids crashing the crash handler when handling a crash outside project
settings lifetime. Instead omitting the configurable message and
continuing with trace dump.
(cherry picked from commit 63068e2ccd)
Using `misc/scripts/fix_headers.py` on all Godot files.
Some missing header guards were added, and the header inclusion order
was fixed in the Bullet module.