overrideConfig API did not notify platform correctly

In the case when overrideConfig was being passed null
to remove any overrides, it was not notifying the system
of the change.

Bug: 131614858
Test: atest GtsTelephonyTestCases
Change-Id: I7e0342c5b2edb9c3f4b0547c424233a4f73733f2
diff --git a/src/com/android/phone/CarrierConfigLoader.java b/src/com/android/phone/CarrierConfigLoader.java
index e2e30ec..ed95a2c 100644
--- a/src/com/android/phone/CarrierConfigLoader.java
+++ b/src/com/android/phone/CarrierConfigLoader.java
@@ -944,10 +944,7 @@
 
         if (overrides == null) {
             mOverrideConfigs[phoneId] = new PersistableBundle();
-            return;
-        }
-
-        if (mOverrideConfigs[phoneId] == null) {
+        } else if (mOverrideConfigs[phoneId] == null) {
             mOverrideConfigs[phoneId] = overrides;
         } else {
             mOverrideConfigs[phoneId].putAll(overrides);