Random crashes when using OGR SQL in -where clause

[Mateusz Łoskot]

The -where clause behaves instable in some cases.
When used against MySQL or PostgreSQL, with OGR dialect of SQL, segmantation fault is thrown.
It should be handled cleanly, if unsupported dialect is used.

Example of crash:

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madmappers:/home/work# /opt/gdal-r11007_x86-linux/bin/ogr2ogr -f MySQL MYSQL:sptest,user=sptest,password=,host=127.0.0.1 -nln locust -update -overwrite FAO_DBsummary.shp -where 'OGR_GEOMETRY=POINT'
Segmentation fault

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1090607360 (LWP 28956)]
0x40357753 in OGRFeature::GetFieldAsString () from /opt/gdal-r11007_x86-linux/lib/libgdal.so.1
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The major goal of this report is to review and fix potential problems with  handling SQL queries in OGR by various ORG drivers.