[macOS] Check for the existence of libMoltenVK

[Langbart]

Check if the libMoltenVK.dylib still exists in the binaries/system/ folder.

reason

• was looking for a bug
• had some problems building
• deleted the binaries/system/ folder and made a clean build
• got some errors when trying to start Vulkan

errors

0 A.D. (0.0.27) Main log (warnings and errors only)
WARNING: Failed to load @executable_path/libMoltenVK.dylib.

ERROR: Unable to create device for Vulkan backend, switching to GL.

Engine exited successfully on 2023-02-08 at 07:37:26 with 1035 message(s), 1 error(s) and 1 warning(s).

workaround

# delete the file
rm -rf libraries/osx/molten-vk/.already-built
# run the script again
./libraries/osx/build-osx-libs.sh
# start vulkan
pyrogenesis -mod=public -mod=0ad-spirv -conf=rendererbackend:vulkan

possible solution

libraries/osx/build-osx-libs.sh

@@ -1048 +1048 @@
 
 mkdir -p "molten-vk"
 pushd "molten-vk" > /dev/null
-if [[ "$force_rebuild" = "true" ]] || [[ ! -e .already-built ]] || [[ "$(<.already-built)" != "$MOLTENVK_VERSION" ]]
+if [[ "$force_rebuild" = "true" ]] || [[ ! -e .already-built ]] || [[ "$(<.already-built)" != "$MOLTENVK_VERSION" ]] || [[ ! -e ../../../binaries/system/libMoltenVK.dylib ]]
 then
   INSTALL_DIR="../../../../binaries/system/"
   rm -f .already-built

[Stan]

In 27541:

Check for the existence of libMoltenVK
Patch by: @Langbart
Fixes #6729