Fix underscrolling problem

The problem is caused by ncurses library rendering only 1000 lines, while
it's possible that we have long messages in the buffer.

Current buffer limit is 200 messages, with just average size of message
of 10 lines, ncurses buffer is being overflown and we render only part
of the message. This causing a problem of "underscrolling": user is unable
to scroll to the top or bottom and he is stuck somewhere in the middle
of the history.

It's not a permanent solution, but rather a temporary fix before
introducing line-counting which will align Profanity's message buffer size
in **lines** with ncurses' limits. It might be even adjustable setting
in the future.

The problem was caused by a faulty logic that 1 message = 1 line and
it's a second try to address it, the try earlier was
ea39657b0a.

src/ui/window.h

@@ -56,7 +56,7 @@
 #include "xmpp/contact.h"
 #include "xmpp/muc.h"
 
-#define PAD_SIZE        1000
+#define PAD_SIZE        10000
 #define LOADING_MESSAGE "Loading older messages…"
 
 void win_move_to_end(ProfWin* window);