Fix buffer overflow

Turns out testing for an empty buffer outside the critical section
wasn't a good idea (testing in a virtual 10 started the thread between
the test and enter, causing buffer overflow in the small loop).

ANSI.c

@@ -184,7 +184,8 @@
     combine multiple CRs as one (to ignore all CRs before LF);
     don't process CR or BS during CRM;
     don't flush CR immediately (to catch following LF);
-    fix CRM with all partial RM sequences.
+    fix CRM with all partial RM sequences;
+    check for the empty buffer within the critical section.
 */
 
 #include "ansicon.h"
@@ -639,10 +640,14 @@ void FlushBuffer( void )
 {
   DWORD nWritten;
 
-  if (nCharInBuffer <= 0) return;
-
   EnterCriticalSection( &CritSect );
 
+  if (nCharInBuffer <= 0)
+  {
+    LeaveCriticalSection( &CritSect );
+    return;
+  }
+
   if (!awm && !im)
   {
     if (pState->crm)

readme.txt

@@ -336,7 +336,8 @@ Version History
 
     1.81-wip - 26 December, 2017:
     - fix multiple CRs before LF (including preventing an immediate flush);
-    - fix CR, BS and partial RM during CRM.
+    - fix CR, BS and partial RM during CRM;
+    - fix buffer overflow caused by incorrect critical section.
 
     1.80 - 24 December, 2017:
     - fix unloading;