If git rev-parse returns an error, set the commit hash to null

compile.bat

@@ -23,7 +23,8 @@ for %%k in (HKCU HKLM) do (
 if %GITFOUND% == yes (
 	set "PATH=%GIT%bin;%PATH%"
 	echo|set /p out="App.Version.commitHash = " > "%~dp0src\002-config\fc-version.js.commitHash.js"
-	git rev-parse --sq --short HEAD >> "%~dp0src\002-config\fc-version.js.commitHash.js"
+	git rev-parse --sq --short HEAD >> "%~dp0src\002-config\fc-version.js.commitHash.js" 2>NUL
+	if errorlevel 1 echo|set /p out="null" >> "%~dp0src\002-config\fc-version.js.commitHash.js"
 	echo|set /p out=";" >> "%~dp0src\002-config\fc-version.js.commitHash.js"
 )