Remove incorrect unreachable usage when guessing DPI factor (#592)

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 - On Windows, non-resizable windows now have the maximization button disabled. This is consistent with behavior on macOS and popular X11 WMs.
+- Corrected incorrect `unreachable!` usage when guessing the DPI factor with no detected monitors.
 
 # Version 0.16.1 (2018-07-02)
 

src/platform/linux/x11/window.rs

@@ -102,7 +102,7 @@ impl UnownedWindow {
                     .unwrap_or(1.0)
             })
         } else {
-            unreachable!("There are no detected monitors, which should've already caused a panic.");
+            return Err(OsError(format!("No monitors were detected.")));
         };
 
         info!("Guessed window DPI factor: {}", dpi_factor);

src/platform/windows/window.rs

@@ -872,7 +872,7 @@ unsafe fn init(
             }
             dpi_factor
         } else {
-            unreachable!("There are no detected monitors, which should've already caused a panic.");
+            return Err(CreationError::OsError(format!("No monitors were detected.")));
         };
         dpi_factor.unwrap_or_else(|| {
             util::get_cursor_pos()