Enable readability-implicit-bool-conversion checks

These checks ensure that we're not implicitly converting ints or
pointers into bools, which makes the code easier to read.

Tested:
Ran series through redfish service validator.  No changes observed.
UUID failing in Qemu both before and after.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I1ca0be980d136bd4e5474341f4fd62f2f6bbdbae
diff --git a/include/security_headers.hpp b/include/security_headers.hpp
index 966fbdf..828a44c 100644
--- a/include/security_headers.hpp
+++ b/include/security_headers.hpp
@@ -25,7 +25,7 @@
                                       "mode=block");
     res.addHeader("X-Content-Type-Options", "nosniff");
 
-    if (!bmcwebInsecureDisableXssPrevention)
+    if (bmcwebInsecureDisableXssPrevention == 0)
     {
         res.addHeader("Content-Security-Policy", "default-src 'none'; "
                                                  "img-src 'self' data:; "