Fix miscellaneous code warnings

libk3bdevice/k3bcdtext.cpp:878: warning: comparison of integer
  expressions of different signedness: 'unsigned int' and 'int'
libk3bdevice/k3bcdtext.cpp:886: warning: comparison of integer
  expressions of different signedness: 'unsigned int' and 'int'

libk3bdevice/k3bdevice.cpp:793: warning: logical 'or' of equal expressions

plugins/decoder/mp3/k3bmad.h:74: warning: 'K3bMad::m_madStructuresInitialized'
  will be initialized after
plugins/decoder/mp3/k3bmad.h:67: warning: 'mad_stream* K3bMad::madStream'
plugins/decoder/mp3/k3bmad.cpp:15: warning: when initialized here

src/rip/k3bpatternparser.h:46: warning: 'void K3b::replaceControlCharacters(QString&)'
  declared 'static' but never defined