Intermittent crash on start on iOS 11 fix

* Crash was due to a bad pointer getting the supper class of the last entry from objc_getClassList
* The 2nd call can sometimes result in the last entry in the array not being initialized fully
     on iOS 11 if more classes are still being loaded into memory.

Author: jkasten2

iOS_SDK/OneSignalSDK/Source/OneSignalSelectorHelpers.m

@@ -90,22 +90,22 @@ void injectToProperClass(SEL newSel, SEL makeLikeSel, NSArray* delegateSubclasse
 }
 
 NSArray* ClassGetSubclasses(Class parentClass) {
-    
     int numClasses = objc_getClassList(NULL, 0);
-    Class *classes = NULL;
+    Class *classes = (Class*)malloc(sizeof(Class) * numClasses);
 
-    classes = (Class *)malloc(sizeof(Class) * numClasses);
-    numClasses = objc_getClassList(classes, numClasses);
+    objc_getClassList(classes, numClasses);
 
     NSMutableArray *result = [NSMutableArray array];
+    
     for (NSInteger i = 0; i < numClasses; i++) {
         Class superClass = classes[i];
+        
         while(superClass && superClass != parentClass) {
             superClass = class_getSuperclass(superClass);
         }
 
-        if (superClass == nil) continue;
-        [result addObject:classes[i]];
+        if (superClass)
+            [result addObject:classes[i]];
     }
 
     free(classes);