Fix bug in MAYBE TRUE/FALSE on void, allow voids to ENSURE

There is no real perceivable harm in letting voids pass tests if
passed to ENSURE, if the tests allow for it.

Also fixes a usage bug of ENSURE in LOAD.

src/core/n-data.c

@@ -207,7 +207,7 @@ REBNATIVE(maybe)
     REBVAL *value = ARG(value);
 
     if (IS_LOGIC(test)) {
-        if (!IS_VOID(test) && VAL_LOGIC(test) == IS_CONDITIONAL_TRUE(value))
+        if (!IS_VOID(value) && VAL_LOGIC(test) == IS_CONDITIONAL_TRUE(value))
             goto type_matched;
         return REF(q) ? R_FALSE : R_BLANK;
     }
@@ -251,10 +251,7 @@ REBNATIVE(maybe)
     // why /? (and its specialization MAYBE?) exist, but to help avoid
     // likely mistakes this returns a void.
     //
-    // Note that in the case of a void passing the test and needing to go
-    // through (e.g. `maybe :void? ()`) will be void also.
-    //
-    if (IS_VOID(value) || IS_CONDITIONAL_FALSE(value))
+    if (IS_CONDITIONAL_FALSE(value))
         return R_VOID;
 
     return R_OUT;

src/mezz/base-funcs.r

@@ -1023,12 +1023,27 @@ ensure: function [
     {Pass through a value only if it matches types (or TRUE?/FALSE? state)}
     return: [<opt> any-value!]
     test [function! datatype! typeset! block! logic!]
-    arg [any-value!] ;-- should <opt> be allowed?
+    arg [<opt> any-value!]
 ][
-    unless maybe? test :arg [
-        fail/where [
-            "ENSURE expected arg to match" (test)
-        ] 'arg
+    case [
+        void? temp: maybe test :arg [
+            assert [any [void? :arg | false? :arg]]
+
+            ; The test passed but we want to avoid an accidental usage like
+            ; `if ensure [logic!] some-false-thing [...]` where the test
+            ; passed but the passthru gets used conditionally.  So FALSE?
+            ; things are converted to void.
+            ;
+            ()
+        ]
+        blank? :temp [
+            fail/where [
+                "ENSURE expected arg to match" (test)
+            ] 'arg
+        ]
+        true [
+            assert [all [true? :temp | :arg = :temp]]
+            :temp
+        ]
     ]
-    :arg
 ]

src/mezz/sys-base.r

@@ -148,7 +148,7 @@ do*: function [
     ;
     ; !!! Should the header always be locked by LOAD?
     ;
-    hdr: lock ensure [object! blank!] first code
+    hdr: lock to-value ensure [object! blank!] first code
     is-module: 'module = select hdr 'type
     code: next code