storage: Need to also VIR_FREE(reg)

Commit-id 'afc4631b' added the regfree(reg) to free resources alloc'd
during regcomp; however, reg still needed to be VIR_FREE()'d. The call
to regfree() also didn't account for possible NULL value.  Reformatted
the call to be closer to usage.
(cherry picked from commit 71da3b66)

Backported to 0.9.12 with afc4631b and its revert skipped.

Signed-off-by: Luca Tettamanti <ltettamanti acunu com>

src/storage/storage_backend_logical.c

@@ -204,13 +204,16 @@ virStorageBackendLogicalMakeVol(virStoragePoolObjPtr pool,
     if (err != 0) {
         char error[100];
         regerror(err, reg, error, sizeof(error));
+        regfree(reg);
         virStorageReportError(VIR_ERR_INTERNAL_ERROR,
                               _("Failed to compile regex %s"),
                               error);
         goto cleanup;
     }
 
-    if (regexec(reg, groups[3], nvars, vars, 0) != 0) {
+    err = regexec(reg, groups[3], nvars, vars, 0);
+    regfree(reg);
+    if (err != 0) {
         virStorageReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                               _("malformed volume extent devices value"));
         goto cleanup;