[flang][runtime] Don't emit empty lines for bad writes

When an error occurs in a formatted sequential output statement
and no output was ever emitted, don't emit a blank record.
This matches the error case behavior of other Fortran compilers.

Differential Revision: https://reviews.llvm.org/D123734

flang/runtime/unit.cpp

@@ -527,6 +527,11 @@ bool ExternalFileUnit::AdvanceRecord(IoErrorHandler &handler) {
       } else {
         // Unformatted stream: nothing to do
       }
+    } else if (handler.GetIoStat() != IostatOk &&
+        furthestPositionInRecord == 0) {
+      // Error in formatted variable length record, and no output yet; do
+      // nothing, like most other Fortran compilers do.
+      return true;
     } else {
       // Terminate formatted variable length record
       const char *lineEnding{"\n"};