Add explicit C++ casts when assigning from void*

C++ requires explicit casts when assign void * return
types like from `malloc`, to a more specific pointer.

xcode/OLMKit/OLMAccount.mm

@@ -83,7 +83,7 @@
 /** public identity keys */
 - (NSDictionary*) identityKeys {
     size_t identityKeysLength = olm_account_identity_keys_length(_account);
-    uint8_t *identityKeysBytes = malloc(identityKeysLength);
+    uint8_t *identityKeysBytes = (uint8_t *)malloc(identityKeysLength);
     if (!identityKeysBytes) {
         return nil;
     }
@@ -124,7 +124,7 @@
 
 - (NSDictionary*) oneTimeKeys {
     size_t otkLength = olm_account_one_time_keys_length(_account);
-    uint8_t *otkBytes = malloc(otkLength);
+    uint8_t *otkBytes = (uint8_t *)malloc(otkLength);
     if (!otkBytes) {
         return nil;
     }

xcode/OLMKit/OLMInboundGroupSession.mm

@@ -38,7 +38,8 @@
     self = [super init];
     if (self)
     {
-        session = malloc(olm_inbound_group_session_size());
+        session = (OlmInboundGroupSession *)
+            malloc(olm_inbound_group_session_size());
         if (session) {
             session = olm_inbound_group_session(session);
         }

xcode/OLMKit/OLMSession.mm

@@ -31,7 +31,7 @@
 
 - (BOOL) initializeSessionMemory {
     size_t size = olm_session_size();
-    _session = malloc(size);
+    _session = (OlmSession *)malloc(size);
     NSParameterAssert(_session != nil);
     if (!_session) {
         return NO;
@@ -235,7 +235,7 @@
         return nil;
     }
     NSString *ciphertextString = [[NSString alloc] initWithData:ciphertext encoding:NSUTF8StringEncoding];
-    OLMMessage *encryptedMessage = [[OLMMessage alloc] initWithCiphertext:ciphertextString type:messageType];
+    OLMMessage *encryptedMessage = [[OLMMessage alloc] initWithCiphertext:ciphertextString type:OLMMessageType(messageType)];
     return encryptedMessage;
 }
 

xcode/OLMKit/OLMUtility.mm

@@ -37,7 +37,7 @@ NSString *const OLMErrorDomain = @"org.matrix.olm";
 
 - (BOOL) initializeUtilityMemory {
     size_t utilitySize = olm_utility_size();
-    _utility = malloc(utilitySize);
+    _utility = (OlmUtility *)malloc(utilitySize);
     NSParameterAssert(_utility != nil);
     if (!_utility) {
         return NO;