Fix: cast caused double free (use mem::forget) (Rust-GPU#105)

Co-authored-by: Döring Christian <christian.doering@ŧum.de>

Author: DoeringChristian

crates/cust/src/memory/device/device_buffer.rs

@@ -314,7 +314,7 @@ impl<A: DeviceCopy + Pod> DeviceBuffer<A> {
     /// whole number of elements. Such as `3` x [`u16`] -> `1.5` x [`u32`].
     /// - If either type is a ZST (but not both).
     #[cfg_attr(docsrs, doc(cfg(feature = "bytemuck")))]
-    pub fn try_cast<B: Pod + DeviceCopy>(self) -> Result<DeviceBuffer<B>, PodCastError> {
+    pub fn try_cast<B: Pod + DeviceCopy>(mut self) -> Result<DeviceBuffer<B>, PodCastError> {
         if align_of::<B>() > align_of::<A>() && (self.buf.as_raw() as usize) % align_of::<B>() != 0
         {
             Err(PodCastError::TargetAlignmentGreaterAndInputNotAligned)
@@ -325,10 +325,12 @@ impl<A: DeviceCopy + Pod> DeviceBuffer<A> {
             Err(PodCastError::SizeMismatch)
         } else if (size_of::<A>() * self.len) % size_of::<B>() == 0 {
             let new_len = (size_of::<A>() * self.len) / size_of::<B>();
-            Ok(DeviceBuffer {
+            let ret = Ok(DeviceBuffer {
                 buf: self.buf.cast(),
                 len: new_len,
-            })
+            });
+            unsafe{std::mem::forget(self);}
+            ret
         } else {
             Err(PodCastError::OutputSliceWouldHaveSlop)
         }