Fix another segfault due to buffer overflow in data/kernels/programs.conf read code
One could cause this by placing line like `perl -e 'print "A"x5000'` in programs.conf
introspection: Helper function to access arrays
Experimental fix for potential Negative array index read in gradiend slider
Coverity CID 1034359
Fix potential out-of-bounds write
However, configstr can not be longer than ~700 chars (see src/control/conf.h, function dt_conf_init), so overflow is unlikely
Coverity CID 1034339
Limit the thumbnail cache sizes to 640x480 max
Merge branch 'master' of https://github.com/darktable-org/darktable