[2019-12-13] - Found with Honggfuzz - CVE-2019-19786

Stack-based buffer overflow in the parse_expr() function, in setparse.c.

Issue can be reproduced by running:

```
atasm test02
```

```
=================================================================
==29838==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff079a8b00 at pc 0x0000004e0478 bp 0x7fff079a8a70 sp 0x7fff079a8a68
WRITE of size 1 at 0x7fff079a8b00 thread T0
    #0 0x4e0477 in parse_expr /home/fcambus/atasm/src/setparse.c:83:13
    #1 0x4e236d in get_signed_expression /home/fcambus/atasm/src/setparse.c:319:5
    #2 0x4e08a5 in get_expression /home/fcambus/atasm/src/setparse.c:154:27
    #3 0x4d3deb in proc_sym /home/fcambus/atasm/src/asm.c:1678:14
    #4 0x4d5556 in do_cmd /home/fcambus/atasm/src/asm.c:1941:5
    #5 0x4d5b46 in assemble /home/fcambus/atasm/src/asm.c:1980:9
    #6 0x4d8082 in main /home/fcambus/atasm/src/asm.c:2392:3
    #7 0x7fad7a5101e2 in __libc_start_main /build/glibc-4WA41p/glibc-2.30/csu/../csu/libc-start.c:308:16
    #8 0x41b3fd in _start (/home/fcambus/atasm/atasm+0x41b3fd)

Address 0x7fff079a8b00 is located in stack of thread T0 at offset 128 in frame
    #0 0x4dfd9f in parse_expr /home/fcambus/atasm/src/setparse.c:71

  This frame has 2 object(s):
    [32, 36) 'v' (line 72)
    [48, 128) 'expr' (line 73) <== Memory access at offset 128 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/fcambus/atasm/src/setparse.c:83:13 in parse_expr
Shadow bytes around the buggy address:
  0x100060f2d110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d150: f1 f1 f1 f1 04 f2 00 00 00 00 00 00 00 00 00 00
=>0x100060f2d160:[f3]f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d170: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 f8 f8 f8 f8
  0x100060f2d180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100060f2d190: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f2 f2 f2 f2
  0x100060f2d1a0: f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00
  0x100060f2d1b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==29838==ABORTING
```