Fix the `/proc/self/status` parser.

[ttldtor]

The parser sometimes parses incorrectly, and in some places allows incorrect values ​​to be parsed.

For example:

Status value	Parsed value	Actual value
Name: VmRSS: 42	42	Key not found
VmRSS: -12 kB	12	Invalid value
VmRSS: garbage42 kB	42	Invalid value
VmRSS: 12 MB	12	Invalid unit
VmRSS: 18446744073709551616 kB	0	Out of range
VmRSS: 18014398509481984 kB	18014398509481984	* 1024 -> Out of range

PLease fix it.