Debug Info: Fix the source range for IfStmt's ConditionScope.

Since the continuation block of the if statement is emitted within the
condition scope this had the undesirable effect of creating a line table
entry at the end of the then or else statement, a line that may have never
been executed.
PR19864 / rdar://problem/17052973

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209764 91177308-0d34-0410-b5e6-96231b3b80d8