Fixed a few c conversions which could crash if they failed

SessionMessagingKit/Crypto/Crypto+SessionMessagingKit.swift

@@ -83,7 +83,8 @@ public extension Crypto.Generator {
                 .unsafeCopyUInt8Array()))
                 .defaulting(to: [])
             var secretKey: [UInt8] = ed25519PrivateKey
-            var cEncryptedDataPtr: UnsafeMutablePointer<UInt8>? = session_encrypt_for_multiple_simple_ed25519(
+            var cDomain: [CChar] = try domain.cString(using: .utf8) ?? { throw LibSessionError.invalidCConversion }()
+            let cEncryptedDataPtr: UnsafeMutablePointer<UInt8>? = session_encrypt_for_multiple_simple_ed25519(
                 &outLen,
                 &cMessages,
                 &messageSizes,
@@ -91,7 +92,7 @@ public extension Crypto.Generator {
                 &cRecipients,
                 recipients.count,
                 &secretKey,
-                domain.cString(using: .utf8),
+                &cDomain,
                 nil,
                 0
             )
@@ -232,13 +233,14 @@ public extension Crypto.Generator {
             var cEncryptedData: [UInt8] = Array(ciphertext)
             var cEd25519PrivateKey: [UInt8] = ed25519PrivateKey
             var cSenderPubkey: [UInt8] = senderSessionId.publicKey
-            var cDecryptedDataPtr: UnsafeMutablePointer<UInt8>? = session_decrypt_for_multiple_simple_ed25519(
+            var cDomain: [CChar] = try domain.cString(using: .utf8) ?? { throw LibSessionError.invalidCConversion }()
+            let cDecryptedDataPtr: UnsafeMutablePointer<UInt8>? = session_decrypt_for_multiple_simple_ed25519(
                 &outLen,
                 &cEncryptedData,
                 cEncryptedData.count,
                 &cEd25519PrivateKey,
                 &cSenderPubkey,
-                domain.cString(using: .utf8)
+                &cDomain
             )
 
             let decryptedData: Data? = cDecryptedDataPtr.map { Data(bytes: $0, count: outLen) }

SessionMessagingKit/Open Groups/Crypto/Crypto+OpenGroupAPI.swift

@@ -139,10 +139,16 @@ public extension Crypto.Verification {
             id: "sessionId",
             args: [standardSessionId, blindedSessionId, serverPublicKey]
         ) {
+            guard
+                var cStandardSessionId: [CChar] = standardSessionId.cString(using: .utf8),
+                var cBlindedSessionId: [CChar] = blindedSessionId.cString(using: .utf8),
+                var cServerPublicKey: [CChar] = serverPublicKey.cString(using: .utf8)
+            else { return false }
+            
             return session_id_matches_blinded_id(
-                standardSessionId.cString(using: .utf8),
-                blindedSessionId.cString(using: .utf8),
-                serverPublicKey.cString(using: .utf8)
+                &cStandardSessionId,
+                &cBlindedSessionId,
+                &cServerPublicKey
             )
         }
     }

SessionSnodeKit/Crypto/Crypto+SessionSnodeKit.swift

@@ -28,9 +28,10 @@ internal extension Crypto.Generator {
             
             guard
                 cNonce.count == 24,
+                var cName: [CChar] = name.lowercased().cString(using: .utf8),
                 session_decrypt_ons_response(
-                    name.lowercased().cString(using: .utf8),
-                    name.count,
+                    &cName,
+                    cName.count,
                     &cCiphertext,
                     cCiphertext.count,
                     &cNonce,