This fixes an edge case where the original label set was done with set_static_text, the next one with set_text and the text is at the same address.
The incomplete check would think that the text resides on heap and it would reallocate it as such, effectively corrupting .data on the next sets.
The manual optimization done dramatically increases performance in software color blending.
Isolated gains reach 20-30%.
Color blending calculates 2 +1 color channels instead of the expensive 1+1+1 calculations.
This is as best as it gets without going in asm optimizations.
