Encode SlaSpace wordsize as an unsigned integer

[mborgerson]

This patch corrects a mismatch between the encoder and decoder in wordsize signedness. AddrSpace::getWordSize() returns an unsigned integer, so use unsigned here for consistency.

Fixes loading SLA files for:

• Toy:BE:32:wordSize2
• Toy:LE:32:wordSize2
• avr8:LE:16:default
• avr8:LE:16:extended
• avr8:LE:16:atmega256
• avr8:LE:24:xmega
• PIC-24E:LE:24:default
• PIC-24F:LE:24:default
• PIC-24H:LE:24:default
• dsPIC30F:LE:24:default
• dsPIC33F:LE:24:default
• dsPIC33E:LE:24:default
• dsPIC33C:LE:24:default
• PIC-16:LE:16:PIC-16C5x
• PIC-12:LE:16:PIC-12C5xx
• PIC-17:LE:16:PIC-17C7xx
• PIC-16:LE:16:PIC-16
• PIC-16:LE:16:PIC-16F
• CP1600:BE:16:default