Fix segfault when closign window while application is loading

Backtrace:
1       0x7f01dd8686d1 armarx::Application::HandlerFault(int) + 961
2       0x7f020502af10 /lib/x86_64-linux-gnu/libc.so.6(+0x3ef10) [0x7f020502af10]
3       0x7f020502ae87 gsignal + 199
4       0x7f020502c7f1 abort + 321
5       0x7f01cb9e6957 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x8c957) [0x7f01cb9e6957]
6       0x7f01cb9ecae6 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x92ae6) [0x7f01cb9ecae6]
7       0x7f01cb9ecb21 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x92b21) [0x7f01cb9ecb21]
8       0x7f01cb9ecd54 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x92d54) [0x7f01cb9ecd54]
9       0x7f01cb9e8a23 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x8ea23) [0x7f01cb9e8a23]
10      0x7f01cba1794c /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xbd94c) [0x7f01cba1794c]
11      0x7f01df28d1ce avi::app::Main::_notification(int) + 350
12      0x7f01df28f8f0 godot_variant godot::__wrapped_method<avi::app::Main, void, int>(void*, void*, void*, int, godot_variant**) + 112
13            0x901d38 arviz-godot() [0x901d38]
14            0x909511 arviz-godot() [0x909511]
15            0xe68c4b arviz-godot() [0xe68c4b]
16            0xe68c6e arviz-godot() [0xe68c6e]
17            0xeb5679 arviz-godot() [0xeb5679]
18           0x21374b3 arviz-godot() [0x21374b3]
19            0x6d00e0 arviz-godot() [0x6d00e0]
20            0x69dd49 arviz-godot() [0x69dd49]
21      0x7f020500dc87 __libc_start_main + 231
22            0x6ad20e arviz-godot() [0x6ad20e]