Add default cases to some switch statements

This squelches several compiler warnings.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/utils.c

@@ -867,6 +867,8 @@ int parse_duration(const char *string, unsigned *duration)
 			case STATE_HHMM_MM:
 				return 0;
 				break;
+			default:
+				break;
 			}
 
 			in = 0;