Fix segfault when reading/writing from paster

handler/paster.go

@@ -66,12 +66,18 @@ func (p *Paster) prepareAndDo(buffer []byte, action func([]byte) (int, error)) (
 
 // Read gets the contents of the paste from the filesystem
 func (p *Paster) Read(buffer []byte) (int, error) {
-	return p.prepareAndDo(buffer, p.file.Read)
+	// Wrap in closure to handle the nil file case
+	return p.prepareAndDo(buffer, func(buffer []byte) (int, error) {
+		return p.file.Read(buffer)
+	})
 }
 
 // Write sets the contents of the paste.
 func (p *Paster) Write(contents []byte) (int, error) {
-	return p.prepareAndDo(contents, p.file.Write)
+	// Wrap in closure to handle the nil file case
+	return p.prepareAndDo(contents, func(buffer []byte) (int, error) {
+		return p.file.Write(buffer)
+	})
 }
 
 // Close closes the paste