isValidMD5() now check length AND hex characters

Changes:

- isValidMD5() now check length AND hex characters.
- code look optimizations.
isValidMD5() check length AND hex characters

Changes:

- isValidMD5() now check length AND hex characters.
- code look optimizations.
isValidMD5() now check length AND hex characters

Changes:

- isValidMD5() now check length AND hex characters.
- code look optimizations.
Merge pull request #374 from abderraouf-adjal/patch-1

isValidMD5() now check length AND hex characters