Log messages for Label Geometry Generator: title and message mixed up

[mstuyts]

Describe the bug

When the expression of a Label Geometry Generator contains an error, a log message is generated. For each expression error a new tab is generated and the tab title contains the error and the message contains date, time and "WARNING Labeling".

How to Reproduce

1. Add a layer to QGIS
2. Enable the Label Styling and Log Messages panels
3. In the layer styling panel go to the label settings
4. Go to the 'Placement' tab in the label settings
5. Enable the 'Geometry generator' checkbox: a first error is generated in the Log Messages panel where the title says 'syntax error, unexpected $end' and the message is '2019-06-25T09:12:21 WARNING Labeling'
6. In the expression window start typing '$geometry': for each typed character a new tab is generated in the Log Messages panel with the following tab titles:
   • syntax error, unexpected Unknown_CHARACTER
   • $g function not known
   • $ge function not known
   • $geo function not known
   • $geom function not known
   • $geome function not known
   • $geomet function not known
   • $geometr function not known

The message in all tabs is something like '2019-06-25T09:12:24 WARNING Labeling' with different times.

QGIS and OS versions
The same results on:

• QGIS version 3.8.0 on Windows 10

QGIS version	3.8.0-Zanzibar	QGIS code revision	11aff65
Compiled against Qt	5.11.2	Running against Qt	5.11.2
Compiled against GDAL/OGR	2.4.1	Running against GDAL/OGR	2.4.1
Compiled against GEOS	3.7.2-CAPI-1.11.0	Running against GEOS	3.7.2-CAPI-1.11.0 b55d2125
PostgreSQL Client Version	9.2.4	SpatiaLite Version	4.3.0
QWT Version	6.1.3	QScintilla2 Version	2.10.8
Compiled against PROJ	5.2.0	Running against PROJ	Rel. 5.2.0, September 15th, 2018
OS Version	Windows 10 (10.0)

• QGIS version 3.8.0 on Ubuntu 18.04.2

QGIS version
3.8.0-Zanzibar
QGIS code revision
11aff65
Compiled against Qt
5.9.5
Running against Qt
5.9.5
Compiled against GDAL/OGR
2.2.3
Running against GDAL/OGR
2.2.3
Compiled against GEOS
3.6.2-CAPI-1.10.2
Running against GEOS
3.6.2-CAPI-1.10.2 4d2925d6
PostgreSQL Client Version
10.9 (Ubuntu 10.9-0ubuntu0.18.04.1)
SpatiaLite Version
4.3.0a
QWT Version
6.1.3
QScintilla2 Version
2.10.2
PROJ.4 Version
493
OS Version
Ubuntu 18.04.2 LTS