libcalamares: improve formatting of Qt error messages

These come through without function information, but we
can format them in one line by mis-using function info.

src/libcalamares/utils/Logger.cpp

@@ -98,18 +98,19 @@ log_implementation( const char* msg, unsigned int debugLevel, const char* funcin
         logfile << date.toUtf8().data() << " - " << time.toUtf8().data() << " [" << debugLevel << "]: " << funcinfo
                 << '\n';
     }
+    if (msg) {
     logfile << date.toUtf8().data() << " - " << time.toUtf8().data() << " [" << debugLevel << (funcinfo ? "]:     " : "]: ") << msg << '\n';
-
+    }
     logfile.flush();
 
     if ( logLevelEnabled( debugLevel ) )
     {
         if ( funcinfo )
         {
-            std::cout << time.toUtf8().data() << " [" << debugLevel << "]: " << funcinfo << s_Continuation;
+            std::cout << time.toUtf8().data() << " [" << debugLevel << "]: " << funcinfo << (msg ? s_Continuation : "");
         }
         // The endl is desired, since it also flushes (like the logfile, above)
-        std::cout << msg << std::endl;
+        std::cout << (msg ? msg : "") << std::endl;
     }
 }
 
@@ -117,20 +118,25 @@ static void
 CalamaresLogHandler( QtMsgType type, const QMessageLogContext&, const QString& msg )
 {
     unsigned int level = LOGVERBOSE;
+    const char * funcinfo = nullptr;
     switch ( type )
     {
     case QtInfoMsg:
         level = LOGVERBOSE;
+        funcinfo = "INFO";
         break;
     case QtDebugMsg:
         level = LOGDEBUG;
+        funcinfo = "DEBUG";
         break;
     case QtWarningMsg:
         level = LOGWARNING;
+        funcinfo = "WARNING";
         break;
     case QtCriticalMsg:
     case QtFatalMsg:
         level = LOGERROR;
+        funcinfo = "ERROR";
         break;
     }
 
@@ -139,7 +145,7 @@ CalamaresLogHandler( QtMsgType type, const QMessageLogContext&, const QString& m
         return;
     }
 
-    log_implementation( msg.toUtf8().constData(), level, nullptr );
+    log_implementation( nullptr, level, (QString(funcinfo) + QStringLiteral(" (Qt): ") + msg).toUtf8().constData() );
 }
 
 QString