LibJS: Reuse as_i32 in as_double in JS::Value

Since this might be complicated with NaN boxing keeping it as one
implementation makes this easier to check and change.

Userland/Libraries/LibJS/Runtime/Value.h

@@ -292,7 +292,7 @@ public:
     {
         VERIFY(is_number());
         if (is_int32())
-            return static_cast<i32>(m_value.encoded);
+            return as_i32();
         return m_value.as_double;
     }