Fixed a bug in memtest progress bar, that had no actual effects.

This closes issue #859, thanks to @erbenmo.

src/memtest.c

@@ -78,10 +78,8 @@ void memtest_progress_end(void) {
 void memtest_progress_step(size_t curr, size_t size, char c) {
     size_t chars = ((unsigned long long)curr*progress_full)/size, j;
 
-    for (j = 0; j < chars-progress_printed; j++) {
-        printf("%c",c);
-        progress_printed++;
-    }
+    for (j = 0; j < chars-progress_printed; j++) printf("%c",c);
+    progress_printed = chars;
     fflush(stdout);
 }