cranelift-wasm: Jump to the destination block at end of consequent

This commit fixes a bug where at the end of an `if..else..end`'s consequent
block, we would sometimes erroneously jump to the `else` block instead of to the
following destination block. Not good!

cranelift/wasmtests/multi-16.wat

@@ -0,0 +1,9 @@
+(module
+  (func (export "param") (param i32) (result i32)
+    (i32.const 1)
+    (if (param i32) (result i32) (local.get 0)
+      (then (i32.const 2) (i32.add))
+      (else (i32.const -2) (i32.add))
+    )
+  )
+)