rbus: fixup null returns in checkmd5

[svc-rdkeportal01]

Fix NULL_RETURNS in checkmd5

Issues Fixed

• Coverity CID 86: NULL_RETURNS in test/rbus/elementTree.c at line 58

Root Cause

fopen() can return NULL if the file cannot be opened (e.g., permission denied, disk full). The original code uses the file pointer without checking for NULL, then attempts to close it, which can cause a segmentation fault.

Changes Made

Added NULL check before using the file pointer returned by fopen():

Before:

FILE* f = fopen(path, "w");
fprintRegisteredElements(f, root, 0);
fclose(f);

After:

FILE* f = fopen(path, "w");

if(!f) {
    printf("%s: Failed to open file %s\n", __FUNCTION__, path);
    return;
}

fprintRegisteredElements(f, root, 0);
fclose(f);

• Line: 58