Add break for default cases

Visual Studio has an option to search all files in a solution, so I
did a search in there for "default:" looking for any missing break
statements.

I've left out default statements that return something, and that throw
something, even if via ThrowInvalidType. UNREACHABLE leads towards throw

R_THROW macro leads towards a return

src/core/hle/service/am/applets/applet_error.cpp

@@ -144,6 +144,7 @@ void Error::Initialize() {
         break;
     default:
         UNIMPLEMENTED_MSG("Unimplemented LibAppletError mode={:02X}!", mode);
+        break;
     }
 }
 

src/core/hle/service/am/applets/applet_general_backend.cpp

@@ -129,6 +129,7 @@ void Auth::Execute() {
     }
     default:
         unimplemented_log();
+        break;
     }
 }
 
@@ -192,6 +193,7 @@ void PhotoViewer::Execute() {
         break;
     default:
         UNIMPLEMENTED_MSG("Unimplemented PhotoViewer applet mode={:02X}!", mode);
+        break;
     }
 }