GIFTranslator: Style fixes
GIFTranslator: Remove unneeded BBitmap checks
GIFTranslator: don't call an implicit constructor for Memblock
GIFTranslator: Style change, uchar => unsigned char
GIFTranslator: Log info messages with LOG_INFO not LOG_ERR
GIFTranslator: Use array notation instead of pointer
GIFTranslator: use ENTRY_COUNT define instead of 4096
GIFTranslator: check if NULL before accessing member
GIFTranslator: Replace magic constants

Introduce GIFPrivate.h to define these magic constants

Also, make sure that we don't go over LZ_MAX_CODE bits
GIFTranslator: Read the left and top image coordinates
GIFTranslator: rename cs and size to codeSize
GIFTranslator: Increase ENTRY_COUNT to 4354

Fixes #10618

Why 4354?

4354 = 4096 + 256 + 1 + 1
4096 for the image data, 256 for the color codes,
1 for the clear code, 1 for the end code
GIFTranslator: error if out of bounds

Error out if we're trying to access an out-of-bounds array index
(which should never happen, but let's check just in case.)