linux-ramdump-parser-v2: Skip bad rodata headers

When checking for rodata differences, we scan the ELF headers of
the vmlinux. Newer vmlinux files seem to have extra ELF headers
with addresses outside the valid mapped range. If we encounter
one of those headers and read an invalid address, skip it.

Change-Id: I2a8af784df7216bf9d890be42eec8599fbaa7f72

linux-ramdump-parser-v2/parsers/roareadiff.py

@@ -57,6 +57,8 @@ class ROData(RamParser):
                         fd.seek(prgheader.offset + (count - prgheader.vaddr))
                         ram_value = self.ramdump.read_word(count)
                         vm_value = struct.unpack('I', fd.read(4))[0]
+                        if ram_value is None:
+                            break
 
                         if detect == 0 and vm_value != ram_value:
                             print_out_str(