SCI: Initialize some members of GfxPaint16 - CID 1010057
SCI: Fix a non-initialized variable in GfxMenu - CID 1003110
SCI: Fix a non-initialized variable in MessageReader - CID 1003120
SCI: Fix a non-initialized variable in MessageState - CID 1003119
SCI: Fix some non-initialized variables in SegManager - CID 1003116
SCI: Fix a non-initialized variable in GfxControls16 - CID 1003114
SCI: Fix a non-initialized variable in GfxCursor - CID 1003112
SCI: Fix a non-initialized variable in GfxScreen - CID 1003105
SCI: Silence some false positive warnings - CID 1003539, 1003540, 1003541, 1003542