Avoid unstable `inner_deref' feature

Author: Dmitry Bogatov

src/dc_chat.rs

@@ -725,7 +725,7 @@ unsafe fn prepare_msg_raw(
                             timestamp,
                             (*msg).type_0,
                             (*msg).state,
-                            (*msg).text.deref().unwrap_or(""),
+                            (*msg).text.as_ref().map(String::as_str).unwrap_or(""),
                             (*msg).param.to_string(),
                             (*msg).hidden,
                             to_string(new_in_reply_to),
@@ -1027,7 +1027,7 @@ unsafe fn set_draft_raw(context: &Context, chat_id: uint32_t, msg: *mut dc_msg_t
                     time(),
                     (*msg).type_0,
                     DC_STATE_OUT_DRAFT,
-                    (*msg).text.deref().unwrap_or(""),
+                    (*msg).text.as_ref().map(String::as_str).unwrap_or(""),
                     (*msg).param.to_string(),
                     1,
                 ],

src/dc_lot.rs

@@ -163,7 +163,10 @@ pub unsafe fn dc_lot_fill(
         }
     }
 
-    let msgtext_c = (*msg).text.deref().map(CString::yolo);
+    let msgtext_c = (*msg)
+        .text
+        .as_ref()
+        .map(|s| CString::yolo(String::as_str(s)));
     let msgtext_ptr = msgtext_c.map(|s| s.as_ptr()).unwrap_or(ptr::null());
 
     (*lot).text2 =

src/dc_mimefactory.rs

@@ -1098,7 +1098,10 @@ unsafe fn get_subject(
     let ret: *mut libc::c_char;
 
     let raw_subject = {
-        let msgtext_c = (*msg).text.deref().map(CString::yolo);
+        let msgtext_c = (*msg)
+            .text
+            .as_ref()
+            .map(|s| CString::yolo(String::as_str(s)));
         let msgtext_ptr = msgtext_c.map(|s| s.as_ptr()).unwrap_or(ptr::null());
 
         dc_msg_get_summarytext_by_raw((*msg).type_0, msgtext_ptr, &mut (*msg).param, 32, context)

src/dc_msg.rs

@@ -834,7 +834,10 @@ pub unsafe fn dc_msg_get_summarytext(
         return dc_strdup(0 as *const libc::c_char);
     }
 
-    let msgtext_c = (*msg).text.deref().map(CString::yolo);
+    let msgtext_c = (*msg)
+        .text
+        .as_ref()
+        .map(|s| CString::yolo(String::as_str(s)));
     let msgtext_ptr = msgtext_c.map(|s| s.as_ptr()).unwrap_or(ptr::null());
 
     dc_msg_get_summarytext_by_raw(

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(c_variadic, ptr_wrapping_offset_from, ptr_cast, inner_deref)]
+#![feature(c_variadic, ptr_wrapping_offset_from, ptr_cast)]
 
 #[macro_use]
 extern crate failure_derive;