calling g2_info() on an incomplete message causes memory error instead of returning error code

[edwardhartnett]

When I call g2_info() on a message before calling g2_gribend() I get a memory error instead of a return code:

=================================================================
==3477==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffdd96a95f6 at pc 0x561d7eaf5ad5 bp 0x7ffdd96a8e20 sp 0x7ffdd96a8e10
READ of size 1 at 0x7ffdd96a95f6 thread T0
    #0 0x561d7eaf5ad4 in gbits /home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/src/gbits.c:75
    #1 0x561d7eaf5ad4 in gbit /home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/src/gbits.c:22
    #2 0x561d7eaf5485 in g2_info /home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/src/g2_info.c:162
    #3 0x561d7eaefe66 in main /home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/tests/tst_g2_addfield.c:96
    #4 0x7f1fedfd30b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #5 0x561d7eaf0dad in _start (/home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/build/tests/tst_g2_addfield+0xddad)

Address 0x7ffdd96a95f6 is located in stack of thread T0 at offset 1334 in frame
    #0 0x561d7eaeee4f in main /home/runner/work/NCEPLIBS-g2c/NCEPLIBS-g2c/g2c/tests/tst_g2_addfield.c:20

  This frame has 15 object(s):
    [48, 56) 'numfields' (line 55)
    [80, 88) 'numlocal' (line 55)
    [112, 116) 'coordlist' (line 46)
    [128, 144) 'listsec0' (line 25)
    [160, 176) 'fld' (line 50)
    [192, 216) 'listsec0_in' (line 54)
    [256, 288) 'bmap' (line 53)
    [320, 360) 'igds' (line 27)
    [400, 440) 'idrstmpl' (line 49)
    [480, 584) 'listsec1' (line 26)
    [624, 728) 'listsec1_in' (line 54)
    [768, 888) 'ipdstmpl' (line 45)
    [928, 1080) 'igdstmpl' (line 28)
    [1152, 1334) 'cgrib' (line 24) <== Memory access at offset 1334 overflows this variable
    [1408, 1590) 'expected_cgrib' (line 29)

The code is written as if it expected to be able to return an error for this:

        if (ipos > (istart + lengrib))
        {
            printf("g2_info: '7777'  not found at end of GRIB message.\n");
            ierr = 5;
            return(ierr);
        }