Silence "libpng warning: iCCP: known incorrect sRGB profile" warnings

These are thrown by 3rd party components (e.g. webkit) which we have no
control over, and have low value anyway

Better to keep the debug log cleaner so that real errors are noticed

src/app/main.cpp

@@ -370,6 +370,12 @@ void myMessageOutput( QtMsgType type, const char *msg )
       myPrint( "Critical: %s\n", msg );
       break;
     case QtWarningMsg:
+    {
+      // Ignore libpng iCPP known incorrect SRGB profile errors
+      // (which are thrown by 3rd party components we have no control over and have low value anyway).
+      if ( strncmp( msg, "libpng warning: iCCP: known incorrect sRGB profile", 50 ) == 0 )
+        break;
+
       myPrint( "Warning: %s\n", msg );
 
 #ifdef QGISDEBUG
@@ -391,6 +397,8 @@ void myMessageOutput( QtMsgType type, const char *msg )
       }
 
       break;
+    }
+
     case QtFatalMsg:
     {
       myPrint( "Fatal: %s\n", msg );