Fix an issue where checking and then unchecking "Suppress leading placeholder" in content filters would not work properly

(code did not properly handle @no vs nil). Issue #2511

Author: dmoagx

Source/SPTableContent.m

@@ -1148,7 +1148,7 @@ - (NSString *)tableFilterString
 	[parser setArgument:[argumentField stringValue]];
 	[parser setFirstBetweenArgument:[firstBetweenField stringValue]];
 	[parser setSecondBetweenArgument:[secondBetweenField stringValue]];
-	[parser setSuppressLeadingTablePlaceholder:(!![filter objectForKey:@"SuppressLeadingFieldPlaceholder"])];
+	[parser setSuppressLeadingTablePlaceholder:[[filter objectForKey:@"SuppressLeadingFieldPlaceholder"] boolValue]];
 	[parser setCaseSensitive:caseSensitive];
 	[parser setCurrentField:[fieldField titleOfSelectedItem]];