patch 9.1.0146: v:echospace wrong with invalid value of 'showcmdloc'

Problem:  v:echospace wrong after setting invalid value to 'showcmdloc'.
Solution: Only call comp_col() if value is valid.
          (zeertzjq)

closes: #14119

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/optionstr.c b/src/optionstr.c
index 771423c..e5f4946 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -3440,8 +3440,12 @@
     char *
 did_set_showcmdloc(optset_T *args UNUSED)
 {
-    comp_col();
-    return did_set_opt_strings(p_sloc, p_sloc_values, FALSE);
+    char	*errmsg = did_set_opt_strings(p_sloc, p_sloc_values, FALSE);
+
+    if (errmsg == NULL)
+	comp_col();
+
+    return errmsg;
 }
 
     int