WT-12006: More robustly place the JS member functions

When placing a JS member on a widget, its name and value are remembered.
This is so that if the value is cleared or replaced, we do so for the
same member function.

There, however, exists a special case for member function where if a
single character is assigned to it, it is replaced by an empty value.
This serves to function such that setting the function to `0` for
example, will result in it being empty.

When we appended the semicolon to it, this caused that last piece of
logic to be ignored, and would generate incorrect JS, which called a
function `0;`.

src/Wt/WWebWidget.C

@@ -902,7 +902,16 @@ void WWebWidget::setJavaScriptMember(const std::string& name,
   std::vector<OtherImpl::Member>& members = *otherImpl_->jsMembers_;
   int index = indexOfJavaScriptMember(name);
 
-  if (index != -1 && (members[index].value == value))
+  // Bug #12006: For safety always append semicolon
+  std::string terminatedValue = value;
+  // Do not escape the value if it is a "default" placeholder.
+  // A value of "0" (or any value of length 1) is converted to an empty
+  // string in setImplementLayoutSizeAware.
+  if (!terminatedValue.empty() && terminatedValue.back() != ';' && terminatedValue != "0") {
+    terminatedValue += ";";
+  }
+
+  if (index != -1 && (members[index].value == terminatedValue))
     return;
 
   if (value.empty()) {
@@ -914,14 +923,10 @@ void WWebWidget::setJavaScriptMember(const std::string& name,
     if (index == -1) {
       OtherImpl::Member m;
       m.name = name;
-      m.value = value;
-      // Bug #12006: For safety always append semicolon
-      if (value.back() != ';') {
-        m.value += ";";
-      }
+      m.value = terminatedValue;
       members.push_back(m);
     } else {
-      members[index].value = value;
+      members[index].value = terminatedValue;
     }
   }