odbccp32: Handle NULL sizeout in SQLGetInstalledDrivers.

dlls/odbccp32/odbccp32.c

@@ -583,7 +583,8 @@ BOOL WINAPI SQLGetInstalledDrivers(char *buf, WORD size, WORD *sizeout)
         return FALSE;
     }
 
-    *sizeout = WideCharToMultiByte(CP_ACP, 0, wbuf, written, NULL, 0, NULL, NULL);
+    if (sizeout)
+        *sizeout = WideCharToMultiByte(CP_ACP, 0, wbuf, written, NULL, 0, NULL, NULL);
     WideCharToMultiByte(CP_ACP, 0, wbuf, written, buf, size, NULL, NULL);
 
     heap_free(wbuf);

dlls/odbccp32/tests/misc.c

@@ -643,6 +643,11 @@ static void test_SQLGetInstalledDrivers(void)
     ok(!ret, "got %d\n", ret);
     check_error(ODBC_ERROR_INVALID_BUFF_LEN);
 
+    ret = SQLGetInstalledDrivers(buffer, 10, NULL);
+    ok(ret, "got %d\n", ret);
+    ok(strlen(buffer) == 8, "got len %u\n", lstrlenA(buffer));
+    ok(!buffer[9], "buffer not doubly null-terminated\n");
+
     ret = SQLGetInstalledDrivers(buffer, 10, &written);
     ok(ret, "got %d\n", ret);
     ok(strlen(buffer) == 8, "got len %u\n", lstrlenA(buffer));