Fix Issue 12449

Undefined format in std.algorithm.max
fix issue 12419

Test that UTF-8 decoding yields a value in the valid range.
UTF-8 may encode values beyond these covered by [0, 0x10FFFF].
Update algorithm.d
Update algorithm.d
Revert
Merge pull request #2038 from blackwhale/issue-12419

Fix issue 12419: assertion failure in std.utf
Merge pull request #2047 from monarchdodra/12449

Fix Issue 12449 - Undefined format in std.algorithm.max