[mlir][tensor] Fix crash when canonicalizing invalid IR (#72888)

This commit fixes a crash of the canonicalizer when there are slice ops
with offset/size SSA values that have a negative constant value. Such
ops are invalid if they are reachable and their offsets/sizes should not
be folded to static integer values. (But such ops may appear in
non-reachable block.)

This commit fixes #71150.