Minor changes to avoid some compilation warnings and two corrections.

[karnute]

The minor changes are:

• Correction of an intended increment operator wrongly typed in video encoder.
• Remove unnecessary intermediate pointer (producing array limits warnings in gcc 6) in wavelet sound decoder by a simpler but equivalent code.
• Prevent excess of null mouse motion events from fractional changes truncated
  to integer in SDL1.2.
• Remove two non-ascii softhyphen characters in comments producing warnings in gcc 6.