WorkAround 12661: To make SortedRange#this() nothrow

Debug statements prevent this function from nothrow.
So I take them out of the function body and put them into the
postcontract which has another context.
Merge pull request #2148 from qchikara/WA12661

FIX 12661: [REG2.066a] std.regex with -debug causes linker errors