Add validation for returncode and fix bracket to standard

[avan989]

Is your feature request related to a problem? Please describe.
Build with options : -Wall -std=c99 -pedantic -Wstrict-prototypes -Wwrite-strings
two warning appear:

/media/sf_share/cFS/tools/elf2cfetbl/elf2cfetbl.c:134:43: warning: missing braces around initializer [-Wmissing-braces]
union Elf_Shdr SectionHeaderStringTable = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
^
{ }
/media/sf_share/cFS/tools/elf2cfetbl/elf2cfetbl.c: In function ‘OpenSrcFile’:
/media/sf_share/cFS/tools/elf2cfetbl/elf2cfetbl.c:1357:9: warning: variable ‘RtnCode’ set but not used [-Wunused-but-set-variable]
int RtnCode;
^~~~~~~

Describe the solution you'd like
First issues, add second bracket:
union Elf_Shdr SectionHeaderStringTable = {{0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }};

second issue:
Add validation for return code.

Requester Info
Anh Van, NASA Goddard