Fix mLoopCount global setting.

The module repeat count is supposed to be configured via mLoopCount
in the Modplug global settings. Setting this to a negative value
is supposed to enable looping forever (what game engines are most
likely to expect), but for some reason, this feature was *deliberately
broken* despite the default being 0. There's no reason for this to
be commented out.

Fixes Konstanty#51

See also:
icculus/SDL_sound#123
https://github.com/AliceLR/megazeux/blob/f83d897dc7df808ed4ad3eb31b5abb6a7b479d08/contrib/patches/libmodplug/01-libmodplug-0.8.9.0-fix-looping.diff

Mainstream pull request: Konstanty#102

Author: AliceLR

src/sndmix.cpp

@@ -360,7 +360,7 @@ BOOL CSoundFile::ProcessRow()
 				// End of song ?
 				if ((m_nPattern == 0xFF) || (m_nCurrentPattern >= MAX_ORDERS))
 				{
-					//if (!m_nRepeatCount)
+					if (!m_nRepeatCount)
 						return FALSE;     //never repeat entire song
 					if (!m_nRestartPos)
 					{
@@ -393,7 +393,7 @@ BOOL CSoundFile::ProcessRow()
 							}
 						}
 					}
-//					if (m_nRepeatCount > 0) m_nRepeatCount--;
+					if (m_nRepeatCount > 0) m_nRepeatCount--;
 					m_nCurrentPattern = m_nRestartPos;
 					m_nRow = 0;
 					if ((Order[m_nCurrentPattern] >= MAX_PATTERNS) || (!Patterns[Order[m_nCurrentPattern]])) return FALSE;