Change the RegisterClass code.

Prevents an issue when creating multiple contexts.

src/win32/init.rs

@@ -31,6 +31,7 @@ pub fn new_window(dimensions: Option<(uint, uint)>, title: &str,
     // This is the only safe method. Using `nosend` wouldn't work for non-native runtime.
     TaskBuilder::new().native().spawn(proc() {
         // registering the window class
+        let class_name = {
             let class_name: Vec<u16> = "Window Class".utf16_units().collect::<Vec<u16>>()
                 .append_one(0);
             
@@ -49,12 +50,14 @@ pub fn new_window(dimensions: Option<(uint, uint)>, title: &str,
                 hIconSm: ptr::mut_null(),
             };
 
-        if unsafe { ffi::RegisterClassExW(&class) } == 0 {
-            use std::os;
-            tx.send(Err(format!("RegisterClassEx function failed: {}",
-                os::error_string(os::errno() as uint))));
-            return;
-        }
+            // We ignore errors because registering the same window class twice would trigger
+            //  an error, and because errors here are detected during CreateWindowEx anyway.
+            // Also since there is no weird element in the struct, there is no reason for this
+            //  call to fail.
+            unsafe { ffi::RegisterClassExW(&class) };
+
+            class_name
+        };
 
         // building a RECT object with coordinates
         let mut rect = ffi::RECT {