bin: Improve error handling in project file lookup
bin: Improve error handling in project file lookup

Previously errors were being silently ignored. Eg, if `rustfmt` did not
have permission to read a `rustfmt.toml` file, the default configuration
was used without informing the user.

graydon/rust,graydon/rust,aidancully/rust,rust-lang/rustfmt,aidancully/rust,flutterhash/rustfmt,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,studoot/rustfmt,SingingTree/rustfmt,aidancully/rust,aidancully/rust,Emilgardis/rustfmt,SingingTree/rustfmt,graydon/rust,graydon/rust,Emilgardis/rustfmt,rust-lang/rustfmt,studoot/rustfmt