Fix handling of CATCH() or FAIL() macros around functions that should return an (akerr_ErrorContext *) but return an invalid pointer (to something not in our exception array)

tests/err_improper_closure.c

@@ -0,0 +1,22 @@
+#include "akerror.h"
+#include <stdio.h>
+
+akerr_ErrorContext AKERR_NOIGNORE *improper_closure(void)
+{
+    PREPARE_ERROR(errctx);
+    ATTEMPT {
+    } CLEANUP {
+    } PROCESS(errctx) {
+    } FINISH(errctx, true);
+    fprintf(stderr, "Improperly returning from improper_closure\n");
+}
+
+int main(void)
+{
+    PREPARE_ERROR(errctx);
+    ATTEMPT {
+	CATCH(errctx, improper_closure());
+    } CLEANUP {
+    } PROCESS(errctx) {
+    } FINISH_NORETURN(errctx);
+}