If the shader contains zero words, we would try to use -1 as an index
into an array at the end of this function, which would be bad. But
shaders without any words are, uh, no point in disassembling in the
first place, so this seems like a theoretical bug in the first place.
However, since the only thing we *really* care about last_next_tag is if
is TAG_BREAK or not, let's initialize it to TAG_BREAK instead. This
means we'll avoid a bogus print at the end here, even if we ended up
calling this on an empty shader.
CID: 1458835
Reviewed-by: Eric R. Smith <eric.smith@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36724>
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