Fix SettingsFontFamily when config is empty

Some device or when Compose preview, the font config is empty.

Use the default font family when the config is empty to fix.

Bug: 235727273
Test: Unit test
Test: Manual with Gallery App
Change-Id: Ifd9c5bbc3d446e5fdb5f393ad994c7545656ead6
diff --git a/packages/SettingsLib/Spa/tests/Android.bp b/packages/SettingsLib/Spa/tests/Android.bp
index 7491045..2449dec 100644
--- a/packages/SettingsLib/Spa/tests/Android.bp
+++ b/packages/SettingsLib/Spa/tests/Android.bp
@@ -31,6 +31,7 @@
         "androidx.compose.runtime_runtime",
         "androidx.compose.ui_ui-test-junit4",
         "androidx.compose.ui_ui-test-manifest",
+        "mockito-target-minus-junit4",
         "truth-prebuilt",
     ],
     kotlincflags: ["-Xjvm-default=all"],