Ignore unknown preprocessor directives which are inside an inactive

conditional (github issue #394, reported by Dan Wilcox).
Regression introduced in 3.0.3.

Examples/test-suite/preproc_defined.i

@@ -107,3 +107,18 @@ void another_macro_checking(void) {
   bumpf(10);
 }
 %}
+
+/* Check that unknown preprocessor directives are ignored inside an inactive
+ * conditional (github issue #394).
+ */
+#ifdef APPLE_OPENGL
+# import <OpenGLES/ES1/gl.h>
+#endif
+#ifdef AAA
+# define B
+#else
+# wibble wibble
+#endif
+#if 0
+# wobble wobble
+#endif