convert to guard statements for readability

SignalServiceKit/src/Contacts/PhoneNumber.m

@@ -324,35 +324,38 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
 
     // Order matters; better results should appear first so prefer
     // matches with the same country code as this client's phone number.
-    OWSAssertDebug(clientPhoneNumber.length > 0);
-    if (clientPhoneNumber.length > 0) {
-        // Note that NBPhoneNumber uses "country code" to refer to what we call a
-        // "calling code" (i.e. 44 in +44123123).  Within SSK we use "country code"
-        // (and sometimes "region code") to refer to a country's ISO 2-letter code
-        // (ISO 3166-1 alpha-2).
-        NSNumber *callingCodeForLocalNumber = [[PhoneNumber phoneNumberFromE164:clientPhoneNumber] getCountryCode];
-        if (callingCodeForLocalNumber != nil) {
-            NSString *callingCodePrefix = [NSString stringWithFormat:@"+%@", callingCodeForLocalNumber];
-
-            tryParsingWithCountryCode(
-                [callingCodePrefix stringByAppendingString:sanitizedString], [self defaultCountryCode]);
-
-            // Try to determine what the country code is for the local phone number
-            // and also try parsing the phone number using that country code if it
-            // differs from the device's region code.
-            //
-            // For example, a French person living in Italy might have an
-            // Italian phone number but use French region/language for their
-            // phone. They're likely to have both Italian and French contacts.
-            NSString *localCountryCode =
-                [PhoneNumberUtil.sharedThreadLocal probableCountryCodeForCallingCode:callingCodePrefix];
-            if (localCountryCode && ![localCountryCode isEqualToString:[self defaultCountryCode]]) {
-                tryParsingWithCountryCode(
-                    [callingCodePrefix stringByAppendingString:sanitizedString], localCountryCode);
-            }
-        }
+    if (clientPhoneNumber.length == 0) {
+        OWSFailDebug(@"clientPhoneNumber had unexpected length");
+        return result;
     }
-    
+
+    // Note that NBPhoneNumber uses "country code" to refer to what we call a
+    // "calling code" (i.e. 44 in +44123123).  Within SSK we use "country code"
+    // (and sometimes "region code") to refer to a country's ISO 2-letter code
+    // (ISO 3166-1 alpha-2).
+    NSNumber *callingCodeForLocalNumber = [[PhoneNumber phoneNumberFromE164:clientPhoneNumber] getCountryCode];
+    if (callingCodeForLocalNumber == nil) {
+        OWSFailDebug(@"callingCodeForLocalNumber was unexpectedly nil");
+        return result;
+    }
+
+    NSString *callingCodePrefix = [NSString stringWithFormat:@"+%@", callingCodeForLocalNumber];
+
+    tryParsingWithCountryCode([callingCodePrefix stringByAppendingString:sanitizedString], [self defaultCountryCode]);
+
+    // Try to determine what the country code is for the local phone number
+    // and also try parsing the phone number using that country code if it
+    // differs from the device's region code.
+    //
+    // For example, a French person living in Italy might have an
+    // Italian phone number but use French region/language for their
+    // phone. They're likely to have both Italian and French contacts.
+    NSString *localCountryCode =
+        [PhoneNumberUtil.sharedThreadLocal probableCountryCodeForCallingCode:callingCodePrefix];
+    if (localCountryCode && ![localCountryCode isEqualToString:[self defaultCountryCode]]) {
+        tryParsingWithCountryCode([callingCodePrefix stringByAppendingString:sanitizedString], localCountryCode);
+    }
+
     return result;
 }