ScriptInfo: fix big bug in the return value logic

The actual return value never got assigned to the implicit "result"
output, because addReturnValue called addItem to add "result" as an
output, which then mistakenly disabled the appendReturnValue flag.
That flag should only be disabled when an _explicit_ output exists.

Author: ctrueden

src/main/java/org/scijava/script/ScriptInfo.java

@@ -432,7 +432,7 @@ private void parseParam(final String param,
 			varName = tokens[1];
 		}
 		final Class<?> type = scriptService.lookupClass(typeName);
-		addItem(varName, type, attrs);
+		addItem(varName, type, attrs, true);
 
 		if (ScriptModule.RETURN_VALUE.equals(varName)) {
 			// NB: The return value variable is declared as an explicit OUTPUT.
@@ -460,11 +460,11 @@ private void checkValid(final boolean valid, final String param)
 	private void addReturnValue() {
 		final HashMap<String, Object> attrs = new HashMap<>();
 		attrs.put("type", "OUTPUT");
-		addItem(ScriptModule.RETURN_VALUE, Object.class, attrs);
+		addItem(ScriptModule.RETURN_VALUE, Object.class, attrs, false);
 	}
 
 	private <T> void addItem(final String name, final Class<T> type,
-		final Map<String, Object> attrs)
+		final Map<String, Object> attrs, final boolean explicit)
 	{
 		final DefaultMutableModuleItem<T> item =
 			new DefaultMutableModuleItem<>(this, name, type);
@@ -477,7 +477,7 @@ private <T> void addItem(final String name, final Class<T> type,
 			registerOutput(item);
 			// NB: Only append the return value as an extra
 			// output when no explicit outputs are declared.
-			appendReturnValue = false;
+			if (explicit) appendReturnValue = false;
 		}
 	}