use if let to avoid potential div by zero

remove semicolon -_-

Add rem_bytes to conditional to avoid error when performing mod by 0

Add test file to confirm compilation passes.

Ensure we don't divide or mod by zero in llvm_type. Include test file from issue.

src/test/ui/issue-50761.rs

@@ -0,0 +1,35 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Confirm that we don't accidently divide or mod by zero in llvm_type
+
+// compile-pass
+
+#![feature(test)]
+
+mod a {
+    pub trait A {}
+}
+
+mod b {
+    pub struct Builder {}
+
+    pub fn new() -> Builder {
+        Builder {}
+    }
+
+    impl Builder {
+        pub fn with_a(&mut self, _a: fn() -> ::a::A) {}
+    }
+}
+
+pub use self::b::new;
+
+fn main() {}