Increment numCompartments on its own line

Andrei noted that incrementing `numCompartments` is more readable if
done on its own line, rather than when indexing an array, in [PR
review](capablevms#88 (comment)). Thanks for the feedback!

example_allocators/compartment_alloc/compartment_alloc.c

@@ -17,31 +17,36 @@ int numCompartments = 0;
 void
 *__capability init_compartment(size_t size_in_bytes, void *__capability dc)
 {
+    void *buf;
+    void *__capability compartment_id;
+
     // We impose a limit on our # of compartments
     if (numCompartments + 1 == maxCompartments) {
         perror("Too many compartments requested.");
         exit(1);
     }
 
     // Allocate memory for this compartment
-    void *buf = mmap(NULL, size_in_bytes, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
+    buf = mmap(NULL, size_in_bytes, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
     if (buf == MAP_FAILED)
     {
         perror("error in initial mem allocation");
         exit(-1);
     }
 
     // Create the new compartment
+    compartment_id = sealed_reference(buf);
     compartments[numCompartments] = (heap_compartment){
-        buf,                     // Space on the heap
-        0,                       // bytes allocated (currently none!)
-        size_in_bytes,           // Our maximum size, to check when allocating
-        dc,                      // The data capability to allocate against (like a DDC)
-        sealed_reference(buf)    // An identifier which allows a holder to allocate in this component
+        buf,              // Space on the heap
+        0,                // bytes allocated (currently none!)
+        size_in_bytes,    // Our maximum size, to check when allocating
+        dc,               // The data capability to allocate against (like a DDC)
+        compartment_id    // An identifier which allows a holder to allocate in this component
     };
+    numCompartments++;
 
     // Return the sealed capability which acts as a token of authentication for a component.
-    return compartments[numCompartments++].identifier;
+    return compartment_id;
 }
 
 /*