ifcfg-rh: fix svSetValue() to properly handle empty variables

svSetValue() called svGetValue() which would return %NULL
for empty variables. That is wrong, because it caused svSetValue()
to add the variable anew.

src/settings/plugins/ifcfg-rh/shvar.c

@@ -382,7 +382,7 @@ svSetValue (shvarFile *s, const char *key, const char *value, gboolean verbatim)
 		newval = value;
 	else
 		newval = svEscape (value, &newval_free);
-	oldval = svGetValue (s, key, FALSE);
+	oldval = svGetValueFull (s, key, FALSE);
 
 	if (!newval || !newval[0]) {
 		/* delete value */