[FIX] blockdom: t-att- correcltly sets the value to zero

In 3536f41f00 we added a fallback when setting a
property to a falsy value so that the property was set to the empty string. The
objective being to not get the string "undefined"/"null"/"false" as property
value. However, using t-att- to set a property to 0 is perfectly reasonable and
in fact quite common.

src/blockdom/attributes.ts

@@ -139,7 +139,8 @@ export function updateClass(this: HTMLElement, val: any, oldVal: any) {
 
 export function makePropSetter(name: string): Setter<HTMLElement> {
   return function setProp(this: HTMLElement, value: any) {
-    (this as any)[name] = value || "";
+    // support 0, fallback to empty string for other falsy values
+    (this as any)[name] = value === 0 ? 0 : value || "";
   };
 }