Try to limit network traffic of map view

There is no reason to keep a connection to a map server when dt is not
in map view. This should be relevant for bug #9816.
Removed check for ambiguous return values for lens lookups.

It can *never* be guaranteed that the return list of lenses of lensfun contains
only one entry, even if the lens model name was exactly correct.  Lenses with a
longer lens name (containing the shorter one) will also be returned.  However,
it is guaranteed that the exact match will be returned as the zeroth list
element.
Merge pull request #469 from bronger/fix_short_lens_names

Removed check for ambiguous return values for lens lookups.
protection against out of memory in masks

more potential fix for #9808
rawspeed: crop garbage pixels for ILCE-7(R) Bug#9818
(cherry picked from commit d9577e4157705012bc64d80279e4f2ced2cd0238)
rawspeed: nikon d5300
(cherry picked from commit d304f2955a515e1dbdd3297f8d0571c1decc8cd2)
Merge https://github.com/darktable-org/darktable
Update