Win32: Fix VS static analysis warnings

src/osmesa_context.c

@@ -47,7 +47,7 @@ static void makeContextCurrentOSMesa(_GLFWwindow* window)
             free(window->context.osmesa.buffer);
 
             // Allocate the new buffer (width * height * 8-bit RGBA)
-            window->context.osmesa.buffer = calloc(4, width * height);
+            window->context.osmesa.buffer = calloc(4, (size_t) width * height);
             window->context.osmesa.width  = width;
             window->context.osmesa.height = height;
         }
@@ -188,7 +188,7 @@ void _glfwTerminateOSMesa(void)
 
 #define setAttrib(a, v) \
 { \
-    assert((size_t) (index + 1) < sizeof(attribs) / sizeof(attribs[0])); \
+    assert(((size_t) index + 1) < sizeof(attribs) / sizeof(attribs[0])); \
     attribs[index++] = a; \
     attribs[index++] = v; \
 }