Update GraphicsMagick to 1.3.34

Why does this need?

[...] This release is the product of significant bug and security fixes due to GraphicsMagick participating in Google's oss-fuzz project. This release fixes 38 issues detected by oss-fuzz (some of which were transient build issues) as well as a number of issues reported via the SourceForge bug tracker, or discovered via testing.

from &2533 (closed)

cf. previous update (!214 (merged))