swf: Pre-allocate the parameters when parsing a `TypeName`

swf/src/avm2/read.rs

@@ -174,7 +174,7 @@ impl<'a> Reader<'a> {
             0x1d => {
                 let base_type = self.read_index()?;
                 let count = self.read_u30()?;
-                let mut parameters = Vec::new();
+                let mut parameters = Vec::with_capacity(count as usize);
 
                 for _ in 0..count {
                     parameters.push(self.read_index()?);