[flang][runtime] Fix nonadvancing output edge case

[klausler]

Summary

When nonadvancing output uses T/TL control edit descriptors to reposition
the record, don't reset the position to the furthest point written at
the end of the write.

flang/runtime/io-stmt.cpp

     if (mutableModes().nonAdvancing) {
       // Make effects of positioning past the last Emit() visible with blanks.
       std::int64_t n{unit().positionInRecord - unit().furthestPositionInRecord};
-      unit().positionInRecord = unit().furthestPositionInRecord;
       while (n-- > 0 && unit().Emit(" ", 1, 1, *this)) {
       }
-      unit().leftTabLimit = unit().furthestPositionInRecord;
+      unit().leftTabLimit = unit().positionInRecord;
     } else {
       unit().AdvanceRecord(*this);
     }