AddRasterConstraints fail with "query string argument of EXECUTE is null"

[strk]

When the target table contains NULL rasters, or no rasters at all. This is a spin-off of #4530.

Known to be bogus in 2.3.8 and later versions

[strk]

In 17936:

Fix AddRasterConstraints in presence of null geoms in table

References #4547 in 2.3 branch

[strk]

In 17937:

Fix AddRasterConstraints in presence of null geoms in table

References #4547 in 2.4 branch

[strk]

In 17938:

Fix AddRasterConstraints in presence of null geoms in table

References #4547 in 2.5 branch

[strk]

In 17939:

Fix AddRasterConstraints in presence of null geoms in table

References #4547 in 3.0 branch

[strk]

In 17942:

Fix AddRasterConstraints in presence of null geoms in table

CLoses #4547 in master branch