[Reflection] Gracefully handle reflection sections with bad sizes.

When a reflection section has a size that only fits a partial record, we detect it, log an error, and abort. However, things like Remote Mirror need to be robust to bad data, so instead handle this by terminating iteration at the last full record.

rdar://91954103

Author: mikeash

include/swift/Reflection/TypeRefBuilder.h

@@ -100,6 +100,12 @@ class ReflectionSectionIteratorBase
     : OriginalSize(Size), Cur(Cur), Size(Size), Name(Name) {
     if (Size != 0) {
       auto NextRecord = this->operator*();
+      if (!NextRecord) {
+        // NULL record pointer, don't attempt to proceed. Setting size to 0 will
+        // make this iterator compare equal to the end iterator.
+        this->Size = 0;
+        return;
+      }
       auto NextSize = Self::getCurrentRecordSize(NextRecord);
       if (NextSize > Size) {
         std::cerr << "!!! Reflection section too small to contain first record\n" << std::endl;
@@ -109,7 +115,9 @@ class ReflectionSectionIteratorBase
                   << ", size of first record: "
                   << NextSize
                   << std::endl;
-        abort();
+        // Set this iterator equal to the end. This section is effectively
+        // empty.
+        this->Size = 0;
       }
     }
   }
@@ -149,14 +157,18 @@ class ReflectionSectionIteratorBase
           std::cerr << std::hex << std::setw(2) << (int)p[i] << " ";
         }
         std::cerr << std::endl;
-        abort();
+        Size = 0; // Set this iterator equal to the end.
       }
     }
 
     return asImpl();
   }
 
   bool operator==(const Self &other) const {
+    // Size = 0 means we're at the end even if Cur doesn't match. This allows
+    // iterators that encounter an incorrect size to safely end iteration.
+    if (Size == 0 && other.Size == 0)
+      return true;
     return Cur == other.Cur && Size == other.Size;
   }