Fixed: TicSpecial could run out of space when writing data

- Fixed: TicSpecial::CheckSpace() never thought it ran out of space due to
  unsigned math.
- Fixed: TicSpecial::GetMoreSpace() assumed only relatively small amounts
  of data would be written at a time so made no effort to ensure it
  actually got enough space. This assumption could be violated by writing
  a very long string, which can happen when replicating a string cvar.

src/d_net.cpp

@@ -185,7 +185,7 @@ static struct TicSpecial
 	size_t used[BACKUPTICS];
 	BYTE *streamptr;
 	size_t streamoffs;
-	int   specialsize;
+	size_t specialsize;
 	int	  lastmaketic;
 	bool  okay;
 
@@ -224,11 +224,11 @@ static struct TicSpecial
 	}
 
 	// Make more room for special commands.
-	void GetMoreSpace ()
+	void GetMoreSpace (size_t needed)
 	{
 		int i;
 
-		specialsize <<= 1;
+		specialsize = MAX(specialsize * 2, needed + 30);
 
 		DPrintf ("Expanding special size to %d\n", specialsize);
 
@@ -240,8 +240,8 @@ static struct TicSpecial
 
 	void CheckSpace (size_t needed)
 	{
-		if (streamoffs >= specialsize - needed)
+		if (streamoffs + needed >= specialsize)
-			GetMoreSpace ();
+			GetMoreSpace (streamoffs + needed);
 
 		streamoffs += needed;
 	}