grib msan issue

[Kurt Schwehr]

I can't figure out this msan issue found by autofuzz

==311057==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x55d36647c9a9 in comunpack frmts/grib/degrib18/g2clib-1.0.4/comunpack.c:82:28
    #1 0x55d36628b45f in g2_unpack7 frmts/grib/degrib18/g2clib-1.0.4/g2_unpack7.c:110:13
    #2 0x55d366274d7d in g2_getfld frmts/grib/degrib18/g2clib-1.0.4/g2_getfld.c:491:16
    #3 0x55d36622b8f7 in unpk_g2ncep tfrmts/grib/degrib18/degrib/grib2api.c:834:11
    #4 0x55d36622ae09 in unpk_grib2 frmts/grib/degrib18/degrib/grib2api.c:1762:7
    #5 0x55d366227595 in ReadGrib2Record frmts/grib/degrib18/degrib/degrib2.cpp:1078:7
    #6 0x55d365fb5ca7 in GRIBRasterBand::ReadGribData(DataSource&, int, int, double**, grib_MetaData**) frmts/grib/gribdataset.cpp:420:5
    #7 0x55d365fb6dd9 in GRIBDataset::Open(GDALOpenInfo*) frmts/grib/gribdataset.cpp:649:13

msan thinks that idrstmpl[12] and idrstmpl[14] are not initialized

[Kurt Schwehr]

msan issue triggered by this file at frmts/grib/degrib18/g2clib-1.0.4/comunpack.c:82

[Even Rouault]

In 39597:

grib / degrib: zero-initialize buffer to avoid MSAN warnings. Fixes #6967. Credit to AutoFuzz

[Kurt Schwehr]

Thanks!