fix: potential in panic message_vector_get_at (#6233)

Description
---
fixes potential in panic message_vector_get_at

Motivation and Context
---
creating the message vector and asking for index[0] will result in a
panic

base_layer/chat_ffi/src/conversationalists.rs

@@ -129,14 +129,15 @@ pub unsafe extern "C" fn conversationalists_vector_get_at(
 
     let conversationalists = &(*conversationalists);
 
-    let len = conversationalists.0.len() - 1;
-    if position as usize > len {
+    let len = conversationalists.0.len();
+    let position = position as usize;
+    if conversationalists.0.is_empty() || position > len - 1 {
         error = LibChatError::from(InterfaceError::PositionInvalidError).code;
         ptr::swap(error_out, &mut error as *mut c_int);
         return ptr::null_mut();
     }
 
-    Box::into_raw(Box::new(conversationalists.0[position as usize].clone()))
+    Box::into_raw(Box::new(conversationalists.0[position].clone()))
 }
 
 /// Frees memory for ConversationalistsVector

base_layer/chat_ffi/src/message.rs

@@ -162,15 +162,16 @@ pub unsafe extern "C" fn chat_metadata_get_at(
 
     let message = &(*message);
 
-    let len = message.metadata.len() - 1;
-    if position as usize > len {
+    let len = message.metadata.len();
+    let position = position as usize;
+    if message.metadata.is_empty() || position > len - 1 {
         error = LibChatError::from(InterfaceError::PositionInvalidError).code;
         ptr::swap(error_out, &mut error as *mut c_int);
         return ptr::null_mut();
     }
 
     let message_metadata_vec = &(*(message).metadata);
-    let message_metadata = Box::new(message_metadata_vec[position as usize].clone());
+    let message_metadata = Box::new(message_metadata_vec[position].clone());
 
     Box::into_raw(message_metadata)
 }

base_layer/chat_ffi/src/messages.rs

@@ -147,15 +147,16 @@ pub unsafe extern "C" fn message_vector_get_at(
     }
 
     let messages = &(*messages);
+    let position = position as usize;
+    let len = messages.0.len();
 
-    let len = messages.0.len() - 1;
-    if position as usize > len {
+    if messages.0.is_empty() || position > len - 1 {
         error = LibChatError::from(InterfaceError::PositionInvalidError).code;
         ptr::swap(error_out, &mut error as *mut c_int);
         return ptr::null_mut();
     }
 
-    Box::into_raw(Box::new(messages.0[position as usize].clone()))
+    Box::into_raw(Box::new(messages.0[position].clone()))
 }
 
 /// Frees memory for MessagesVector

base_layer/wallet_ffi/src/lib.rs

@@ -2506,8 +2506,8 @@ pub unsafe extern "C" fn seed_words_get_at(
         error = LibWalletError::from(InterfaceError::NullError("seed words".to_string())).code;
         ptr::swap(error_out, &mut error as *mut c_int);
     } else {
-        let len = (*seed_words).0.len() - 1; // clamp to length
-        if position > len as u32 {
+        let len = (*seed_words).0.len(); // clamp to length
+        if (*seed_words).0.is_empty() || position > (len - 1) as u32 {
             error = LibWalletError::from(InterfaceError::PositionInvalidError).code;
             ptr::swap(error_out, &mut error as *mut c_int);
         } else if let Ok(v) = CString::new(