PR 49214 fd_gets should return NULL if nothing was read

From-SVN: r174395

libgfortran/ChangeLog

@@ -1,3 +1,8 @@
+2011-05-29  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR libfortran/49214
+	* runtime/backtrace.c (fd_gets): Return NULL if nothing was read.
+
 2011-05-29  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	PR libfortran/19155

libgfortran/runtime/backtrace.c

@@ -95,6 +95,8 @@ fd_gets (char *s, int size, int fd)
       else
 	{
 	  s[i] = '\0';
+	  if (i == 0)
+	    return NULL;
 	  break;
 	}
     }