cairogradient segfault in ASAN test

[jaromil]

Running #153 detected this:

{
 "name":"cairogradient",
 "type":"filter",
 "color_model":"rgba8888",
 "num_params":"11"
},
 "parameters":[
  {"name":"pattern","type":"string","explanation":"Linear or radial gradient"},
  {"name":"start color","type":"color","explanation":"First color of the gradient"},
  {"name":"start opacity","type":"double","explanation":"Opacity of the first color of the gradient"},
  {"name":"end color","type":"color","explanation":"Second color of the gradient"},
  {"name":"end opacity","type":"double","explanation":"Opacity of the second color of the gradient"},
  {"name":"start x","type":"double","explanation":"X position of the start point of the gradient"},
  {"name":"start y","type":"double","explanation":"Y position of the start point of the gradient"},
  {"name":"end x","type":"double","explanation":"X position of the end point of the gradient"},
  {"name":"end y","type":"double","explanation":"Y position of the end point of the gradient"},
  {"name":"offset","type":"double","explanation":"Position of first color in the line connecting gradient ends, really useful only for radial gradient"},
  {"name":"blend mode","type":"string","explanation":"Blend mode used to compose gradient on image. Accepted values: 'normal', 'add', 'saturate', 'multiply', 'screen', 'overlay', 'darken', 'lighten', 'colordodge', 'colorburn', 'hardlight', 'softlight', 'difference', 'exclusion', 'hslhue', 'hslsaturation', 'hslcolor', 'hslluminosity'"}
 ]
}
AddressSanitizer:DEADLYSIGNAL
=================================================================
==23738==ERROR: AddressSanitizer: SEGV on unknown address (pc 0x7f6dfdb71119 bp 0x7ffd09b21930 sp 0x7ffd09b210d8 T0)
==23738==The signal is caused by a READ memory access.
==23738==Hint: this fault was caused by a dereference of a high value address (see register values below).  Disassemble the provided pc to learn which register was used.
    #0 0x7f6dfdb71119  (/lib/x86_64-linux-gnu/libc.so.6+0x167119) (BuildId: def5460e3cee00bfee25b429c97bcc4853e5b3a8)
    #1 0x7f6dfe078ee9 in strlen ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:389
    #2 0x7f6dfe6c9afa in f0r_set_param_value /home/jrml/devel/frei0r/src/filter/cairogradient/cairogradient.c:181
    #3 0x5579d82e7dcd in test_parameters(void*, void (*)(void*, void*, int), void (*)(f0r_param_info*, int), int, int) /home/jrml/devel/frei0r/test/frei0r-run.c:171
    #4 0x5579d82e88ed in main /home/jrml/devel/frei0r/test/frei0r-run.c:370
    #5 0x7f6dfda33ca7  (/lib/x86_64-linux-gnu/libc.so.6+0x29ca7) (BuildId: def5460e3cee00bfee25b429c97bcc4853e5b3a8)
    #6 0x7f6dfda33d64 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29d64) (BuildId: def5460e3cee00bfee25b429c97bcc4853e5b3a8)
    #7 0x5579d82e7260 in _start (/home/jrml/devel/frei0r/test/frei0r-run+0x3260) (BuildId: a01640d73d2b6b674124aa6fc0fa8fdab427fa36)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x167119) (BuildId: def5460e3cee00bfee25b429c97bcc4853e5b3a8)
==23738==ABORTING