Fix non-existent cache on first run breaking locking

src/imapdomo.skel

@@ -97,6 +97,7 @@ lock() {
     #
     debug -v NoLock
     $NoLock && return 0
+    mkdir -p "$IMAPDOMO_USER_CACHE"
     date +"$$@%s" > "$IMAPDOMO_USER_CACHE/lock"
     debug -f "$IMAPDOMO_USER_CACHE/lock"
 }