If ferror is true, we must reset the error indicator.

Submitted by:	Liam J. Foy <liamfoy@sepulcrum.org>
Approved by:	grehan (mentor)

usr.bin/rev/rev.c

@@ -103,6 +103,7 @@ main(int argc, char *argv[])
 		}
 		if (ferror(fp)) {
 			warn("%s", filename);
+			clearerr(fp);
 			rval = 1;
 		}
 		(void)fclose(fp);