Fix readline() when fgets returns NULL even on success

Signed-off-by: Rafael Ravedutti <rafaelravedutti@gmail.com>

common/util.c

@@ -4,6 +4,7 @@
  * Use of this source code is governed by a LGPL-3.0
  * license that can be found in the LICENSE file.
  */
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -84,7 +85,9 @@ int get_num_threads() {
 
 void readline(char *line, FILE *fp) {
     if(fgets(line, MAXLINE, fp) == NULL) {
-        fprintf(stderr, "readline(): Error: could not read line!\n");
+        if(errno != 0) {
+            perror("readline()");
             exit(-1);
         }
     }
+}