commit 0011432dda4d0968823df8fecde6e5a828b72966
Author: Peter Urbanec <winehq.org@urbanec.net>
Date:   Wed Jan 7 10:31:07 2009 +1100

    wintab32: Check for NULL before using context.

diff --git a/dlls/wintab32/context.c b/dlls/wintab32/context.c
index efc5cfa..b2a9c98 100644
--- a/dlls/wintab32/context.c
+++ b/dlls/wintab32/context.c
@@ -702,6 +702,12 @@ BOOL WINAPI WTOverlap(HCTX hCtx, BOOL fToTop)
 
     EnterCriticalSection(&csTablet);
     context = TABLET_FindOpenContext(hCtx);
+    if (!context)
+    {
+        LeaveCriticalSection(&csTablet);
+        return FALSE;
+    }
+
     /* if we want to send to top and it's not already there */
     if (fToTop && context->context.lcStatus != CXS_ONTOP)
     {
@@ -806,6 +812,12 @@ BOOL WINAPI WTSetA(HCTX hCtx, LPLOGCONTEXTA lpLogCtx)
 
     EnterCriticalSection(&csTablet);
     context = TABLET_FindOpenContext(hCtx);
+    if (!context)
+    {
+        LeaveCriticalSection(&csTablet);
+        return FALSE;
+    }
+
     LOGCONTEXTAtoW(lpLogCtx, &context->context);
     LeaveCriticalSection(&csTablet);
 
@@ -828,6 +840,12 @@ BOOL WINAPI WTSetW(HCTX hCtx, LPLOGCONTEXTW lpLogCtx)
 
     EnterCriticalSection(&csTablet);
     context = TABLET_FindOpenContext(hCtx);
+    if (!context)
+    {
+        LeaveCriticalSection(&csTablet);
+        return FALSE;
+    }
+
     memmove(&context->context, lpLogCtx, sizeof(LOGCONTEXTW));
     LeaveCriticalSection(&csTablet);