patch 9.0.1734: :runtime completion fails for multiple args

Problem: :runtime completion fails for multiple args
Solution: Make it work

closes: #12616

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/scriptfile.c b/src/scriptfile.c
index 37d57e5..2aca346 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -289,6 +289,15 @@
     char_u  *p = skiptowhite(arg);
     runtime_expand_flags
 	= *p != NUL ? get_runtime_cmd_flags(&arg, p - arg) : 0;
+    // Skip to the last argument.
+    while (*(p = skiptowhite_esc(arg)) != NUL)
+    {
+	if (runtime_expand_flags == 0)
+	    // When there are multiple arguments and [where] is not specified,
+	    // use an unrelated non-zero flag to avoid expanding [where].
+	    runtime_expand_flags = DIP_ALL;
+	arg = skipwhite(p);
+    }
     xp->xp_context = EXPAND_RUNTIME;
     xp->xp_pattern = arg;
 }