Heap-use-after-free in range_union on a fuzzed xls file.

Git versions of glib, goffice, gnumeric, libgsf and libxml2.

Test case: http://jutaky.com/fuzzing/gnumeric_case_29042_5897.xls

==13866== ERROR: AddressSanitizer: heap-use-after-free on address 0x6004002028f0 at pc 0x7ff7fe727907 bp 0x7fff79829c70 sp 0x7fff79829c68
READ of size 4 at 0x6004002028f0 thread T0
    #0 0x7ff7fe727906 in range_union /gnumeric/src/ranges.c:540
    #1 0x7ff7dbdcd576 in excel_read_MERGECELLS /gnumeric/plugins/excel/ms-excel-read.c:4867
    #2 0x7ff7dbde8bba in excel_read_sheet /gnumeric/plugins/excel/ms-excel-read.c:6694
    #3 0x7ff7dbdec6b0 in excel_read_BOF /gnumeric/plugins/excel/ms-excel-read.c:6991
    #4 0x7ff7dbdedd5e in excel_read_workbook /gnumeric/plugins/excel/ms-excel-read.c:7081
    #5 0x7ff7dbd63bfc in excel_enc_file_open /gnumeric/plugins/excel/boot.c:193
    #6 0x7ff7dbd6489a in excel_file_open /gnumeric/plugins/excel/boot.c:250
    #7 0x7ff7fd7f4fde in go_plugin_loader_module_func_file_open /goffice/goffice/app/go-plugin-loader-module.c:282
    #8 0x7ff7fd7fdf40 in go_plugin_file_opener_open /goffice/goffice/app/go-plugin-service.c:685 (discriminator 1)
    #9 0x7ff7fd80a88f in go_file_opener_open /goffice/goffice/app/file.c:417
    #10 0x7ff7fe960684 in workbook_view_new_from_input /gnumeric/src/workbook-view.c:1281
    #11 0x7ff7fe960e73 in workbook_view_new_from_uri /gnumeric/src/workbook-view.c:1341
    #12 0x40a6e0 in main /gnumeric/src/main-application.c:322
    #13 0x7ff7f90e8bc4 in __libc_start_main ??:?
    #14 0x403de8 in _start ??:?
0x6004002028f0 is located 0 bytes inside of 16-byte region [0x6004002028f0,0x600400202900)

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Juha Kylmänen
Research Assistant, OUSPG