winex11.drv: Declare variable signed to accept possible negative return value (Coverity)

[Andrew Talbot]

nAttribs accepts the return value of ConvertAttribWGLtoGLX(), which will be negative in the
event of an error. This patch should fix CID-245.

-- Andy.
---
Changelog:
   winex11.drv: Declare variable signed to accept possible negative return value (Coverity).

diff -urN a/dlls/winex11.drv/opengl.c b/dlls/winex11.drv/opengl.c
--- a/dlls/winex11.drv/opengl.c	2007-01-25 17:28:42.000000000 +0000
+++ b/dlls/winex11.drv/opengl.c	2007-02-03 22:16:36.000000000 +0000
@@ -1923,7 +1923,7 @@
     GLXFBConfig* cfgs = NULL;
     int nCfgs = 0;
     int attribs[256];
-    unsigned nAttribs = 0;
+    int nAttribs = 0;
     int fmt_index = 0;
 
     TRACE("(%p, %d, %d, %d, %p)\n", hdc, iPixelFormat, iWidth, iHeight, piAttribList);