plugins/nightlight: Guard against invalid timings in the config

Morning and evening timings should be ordered correctly. When computing
the daylight duration, that ternary operator should not be needed and it
hides other bugs.

src/plugins/nightlight/nightlightmanager.cpp

@@ -279,8 +279,12 @@ void NightLightManager::readConfig()
     // fixed timings
     QTime mrB = QTime::fromString(s->morningBeginFixed(), "hhmm");
     QTime evB = QTime::fromString(s->eveningBeginFixed(), "hhmm");
+    if (mrB >= evB) {
+        mrB = QTime(6, 0);
+        evB = QTime(18, 0);
+    }
 
-    int diffME = evB > mrB ? mrB.msecsTo(evB) : evB.msecsTo(mrB);
+    int diffME = mrB.msecsTo(evB);
     int diffMin = std::min(diffME, MSC_DAY - diffME);
 
     int trTime = s->transitionTime() * 1000 * 60;