Fix cache test reenable loop in VC_EVENT_READ_READY handler (#12712)

Move process_event() call outside the while loop that consumes data blocks.
The original code was calling reenable() for every block of data, which is
incorrect. The correct pattern (as shown in CacheTestSM) is to consume all
available data, then call reenable() once to signal readiness for more.

This fixes the flaky test_cache_Populated_Cache test that was aborting due
to excessive reenables when reading from a populated cache with many blocks.

Author: bryancall

src/iocore/cache/unit_tests/main.cc

@@ -319,19 +319,23 @@ CacheReadTest::read_event(int event, void *e)
     this->process_event(event);
     break;
   case VC_EVENT_READ_READY: {
+    // Consume all available data blocks and validate against expected data
     while (this->_reader->block_read_avail()) {
       auto str = this->_reader->block_read_view();
       if (memcmp(str.data(), this->_cursor, str.size()) == 0) {
         this->_reader->consume(str.size());
         this->_cursor += str.size();
-        this->process_event(event);
       } else {
+        // Data corruption detected - fail the test immediately
         CHECK(false);
         this->close();
         TEST_DONE();
-        break;
+        return 0;
       }
     }
+    // After consuming all available data, reenable the VIO to signal readiness for more.
+    // This should only be called once per VC_EVENT_READ_READY event, not per-block.
+    this->process_event(event);
     break;
   }
   case VC_EVENT_ERROR: