Win32: Make Setup/Update Mutex theme-unique

Fixes #3272

cmake/modules/NSIS.template.in

@@ -777,7 +777,7 @@ Function .onInit
       goto UAC_Elevate
 
    ;Prevent multiple instances.
-   System::Call 'kernel32::CreateMutexA(i 0, i 0, t "owncloudInstaller") i .r1 ?e'
+   System::Call 'kernel32::CreateMutexA(i 0, i 0, t "${APPLICATION_SHORTNAME}Installer") i .r1 ?e'
    Pop $R0
    StrCmp $R0 0 +3
       MessageBox MB_OK|MB_ICONEXCLAMATION $INIT_INSTALLER_RUNNING