pdump: check missing home environment variable

pdump: check missing home environment variable

inside pdump_get_socket_path(), getenv can return
a NULL pointer if the match for SOCKET_PATH_HOME is
not found in the environment. NULL check is added to
return -1 immediately. Since pdump_get_socket_path()
returns -1 now, wherever this function is called
there the return value is checked and error message
is logged.

Coverity issue: 127344, 127347

Fixes: 278f945402c5 ("pdump: add new library for packet capture")
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>