patch 8.2.4821: crash when imported autoload script was deleted

Problem:    Crash when imported autoload script was deleted.
Solution:   Initialize local variable. (closes #10274)  Give a more meaningful
            error message.
diff --git a/src/eval.c b/src/eval.c
index 61b09fb..f7445bf 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -6159,7 +6159,7 @@
 	    char_u	*exp_name;
 	    int		cc;
 	    int		idx;
-	    ufunc_T	*ufunc;
+	    ufunc_T	*ufunc = NULL;
 	    type_T	*type;
 
 	    // Found script from "import {name} as name", script item name must