Check for end of input while reading expressions (WebAssembly#8092)

If the input ends in an expression, we are missing at minimum the end
of the function, so it is definitely invalid.

Fixes WebAssembly#8089

Author: kripken

src/wasm/wasm-binary.cpp

@@ -4763,12 +4763,15 @@ void WasmBinaryReader::readExports() {
 
 Expression* WasmBinaryReader::readExpression() {
   assert(builder.empty());
-  while (input[pos] != BinaryConsts::End) {
+  while (more() && input[pos] != BinaryConsts::End) {
     auto inst = readInst();
     if (auto* err = inst.getErr()) {
       throwError(err->msg);
     }
   }
+  if (!more()) {
+    throwError("unexpected end of input");
+  }
   ++pos;
   auto expr = builder.build();
   if (auto* err = expr.getErr()) {