There are two errors: 1) If find is set to search for files that were changed
in the last n days but n is not a number (-ctime x), then find complains about
a ”missing” argument instead of reporting the ”incorrect” argument. Function
parse_time calls collect_args to assign the current argument argv[*arg_ptr] to
timearg and increment the argument pointer arg_ptr (parser.c:3102). When
timearg is failed to be parsed as a number, parse_time returns without
decrementing arg_ptr (parser.c:3127-3128). When the error is reported
(tree.c:1248-1271), the argument pointer points to NULL directly after the
incorrect argument (tree.c:1250), such that the error is reported as missing
argument instead of invalid argument. 2) If find is set to search for files
belonging to a certain group but the group-id is not specified or not a number
(-gid x), then find crashes with a segmentation fault. When the argument
following the -gid option is being parsed (parser.c:913), insert num returns
NULL because argv[*arg_ptr] is NULL or not a number (parser.c:3235-3259). This
nullpointer remains unchecked and is dereferenced leading to a segmentation
fault (parser.c:914). When nullpointer dereference is fixed the same symptom is
observed for -gid as for -ctime because the argument pointer is also forgot to
be decremented. 

Examples of Correct Fixes: 
For first error, 
1) decrement/restore arg_ptr when parsing of second argument of an option fails,
2) use copy of old argument during error-reporting. 

For second error, add null pointer check. 

Example of Incorrect Fix:
For first error, decrement argument pointer before even calling parse_time
(Regression because even correct arguments are reported as incorrect ones).
