Fix PR 103317, ICE after PHI-OPT, minmax_replacement producing invalid SSA

Fix PR 103317, ICE after PHI-OPT, minmax_replacement producing invalid SSA

The problem is r12-5300-gf98f373dd822b35c allows phiopt to recognize more basic blocks
but missed one location where the basic block does not need to be empty but still
needs to have a single predecessor. This patch fixes that over sight.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/103317

gcc/ChangeLog:

	* tree-ssa-phiopt.c (minmax_replacement): For the non empty
	middle bb case, check to make sure it has a single predecessor.

gcc/testsuite/ChangeLog:

	* gcc.c-torture/compile/pr103317-1.c: New test.