patch 8.2.4653: "import autoload" does not check the file name

Problem:    "import autoload" does not check the file name.
Solution:   Give an error if the file is not readable. (closes #10049)
diff --git a/src/spellfile.c b/src/spellfile.c
index ad0d000..aaacb2e 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -5976,7 +5976,7 @@
 	}
 	if (mch_isdir(wfname))
 	{
-	    semsg(_(e_src_is_directory), wfname);
+	    semsg(_(e_str_is_directory), wfname);
 	    goto theend;
 	}