cut, mount: small improvements

libbb/get_line_from_file.c

@@ -41,6 +41,7 @@ char *bb_get_chunk_from_file(FILE * file, int *end)
 			free(linebuf);
 			return NULL;
 		}
+		linebuf = xrealloc(linebuf, idx+1);
 		linebuf[idx] = 0;
 	}
 	return linebuf;