src/io.c: Null-terminate the ical_readline() buffer

Ensure we always return with a null-terminated buffer, even if we read
more than BUFSIZ characters.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/io.c

@@ -1896,6 +1896,7 @@ ical_readline (FILE *fdi, char *buf, char *lstore, unsigned *ln)
       if (*lstore != SPACE && *lstore != TAB)
         break;
       strncat (buf, lstore + 1, BUFSIZ);
+      buf[BUFSIZ - 1] = '\0';
       (*ln)++;
     }