Auto merge of #1112 - emilio:always-gen, r=pepyakin
Auto merge of #1112 - emilio:always-gen, r=pepyakin

lib: Always generate bindings.

Some cases in spawning rustfmt were not properly returning the source. Make it
more reliable.

This hit me when trying to update bindgen in Firefox.

emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen