Fix file error reporting.

Not sure why exceptions don't have that info… 🤷

src/main.cpp

@@ -32,6 +32,7 @@
 #include <cmath>
 #include <cstdint>
 #include <cstdlib>
+#include <cstring>
 #include <exception>
 #include <fstream>
 #include <future>
@@ -158,12 +159,11 @@ int main(int argc, char *argv[])
                 }
                 catch (const std::ifstream::failure &e)
                 {
-                    // std::ifstream seems to always return a generic error?
                     LOG(lg, log::sev::error)
-                        << translate("Probably permission denied.") << " ("
-                        << e.what() << ')'
+                        << std::strerror(errno)
                         << format(translate(" (while opening {0:s})").str(),
                                   filepath);
+                    return EXIT_FAILURE;
                 }
             }