FIXED: #1097 ctrl-C in read causes exit from REPL

Fix consists of two parts.  (1) if something (libedit) already set the
stream error condition, make S__fillbuf() return with an error immediately
and (2) do not abort the main query loop if we get an abort request.

src/os/pl-stream.c

@@ -679,6 +679,8 @@ S__fillbuf(IOSTREAM *s)
       { if ( !(s->flags & SIO_NOFEOF) )
 	  s->flags |= SIO_FEOF;
 	return -1;
+      } else if ( Sferror(s) )
+      { return -1;
 #ifdef EWOULDBLOCK
       } else if ( errno == EWOULDBLOCK )
       { s->bufp = s->buffer;

src/pl-pro.c

@@ -154,7 +154,10 @@ query_loop(atom_t goal, int loop)
     }
 
     if ( !rc && (except = PL_exception(qid)) )
-    { if ( Sferror(Suser_input) ||
+    { if ( classify_exception(except) == EXCEPT_ABORT )
+	Sclearerr(Suser_input);
+
+      if ( Sferror(Suser_input) ||
 	   Sferror(Suser_output) ||
 	   Sferror(Suser_error) )
 	return -1;