graphicsmagick/coder_WPG_fuzzer: Unknown signal in InsertRow

Project:
http://hg.code.sf.net/p/graphicsmagick/code

Detailed report: https://oss-fuzz.com/testcase?key=4875204321869824

Project: graphicsmagick
Fuzzer: libFuzzer_graphicsmagick_coder_WPG_fuzzer
Fuzz target binary: coder_WPG_fuzzer
Job Type: libfuzzer_ubsan_graphicsmagick
Platform Id: linux

Crash Type: Unknown signal
Crash Address: 0x000000000000
Crash State:
InsertRow
UnpackWPG2Raster
ReadWPGImage

Sanitizer: undefined (UBSAN)

Regressed: https://oss-fuzz.com/revisions?job=libfuzzer_ubsan_graphicsmagick&range=201804110537:201804120543

Reproducer Testcase: https://oss-fuzz.com/download?testcase_id=4875204321869824

Issue filed automatically.

See https://github.com/google/oss-fuzz/blob/master/docs/reproducing.md for more information.

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