[Relax] Fix divide-by-zero in reshape pattern detection

[guan404ming]

Why

Fixes #17745. has_reshape_pattern builds an inverse index map that divides by each iter extent, so a zero-extent iter crashed with divide-by-zero.

How

• Skip the fused-var check when any block iter has zero extent; such blocks touch no elements, so they are not reshape patterns.
• Added test_reshape_pattern_zero_extent in tests/python/relax/test_analysis.py.

[gemini-code-assist]

Code Review

This pull request prevents division-by-zero crashes during reshape pattern analysis by skipping checks on blocks with zero-extent iterators, and adds a unit test to verify this behavior. The reviewer suggested using the analyzer's CanProveEqual method instead of is_zero to robustly handle symbolic zero extents as well as constant ones.

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[gemini-code-assist]

Using is_zero only checks if the extent is a constant integer 0. If the extent is a symbolic expression that can be proven to be 0 by the analyzer, is_zero will return false, which could still lead to a division-by-zero crash during the subsequent inverse index map simplification.

Since the analyzer ana_ is already available, we can use this->ana_->CanProveEqual(v->dom->extent, 0) to robustly handle both constant and symbolic zero extents.

Suggested change

	bool has_zero_extent = std::any_of(block->iter_vars.begin(), block->iter_vars.end(),
	[](const IterVar& v) { return is_zero(v->dom->extent); });
	bool has_zero_extent = std::any_of(block->iter_vars.begin(), block->iter_vars.end(),
	[this](const IterVar& v) { return this->ana_->CanProveEqual(v->dom->extent, 0); });