dbghelp: Add a return statement for the default/assert case in elf_map_file.

dlls/dbghelp/elf_module.c

@@ -294,6 +294,7 @@ static BOOL elf_map_file(struct elf_map_file_data* emfd, struct image_file_map*
         filename = NULL;
         break;
     default: assert(0);
+        return FALSE;
     }
 
     elf_reset_file_map(fmap);