Check return value on write of raw pointer

objectivec/GPBCodedOutputStream.m

@@ -942,7 +942,10 @@ static void GPBWriteRawLittleEndian64(GPBOutputBufferState *state,
       state_.position = length;
     } else {
       // Write is very big.  Let's do it all at once.
-      [state_.output write:((uint8_t *)value) + offset maxLength:length];
+      NSInteger written = [state_.output write:((uint8_t *)value) + offset maxLength:length];
+      if (written != (NSInteger)length) {
+        [NSException raise:GPBCodedOutputStreamException_WriteFailed format:@""];
+      }
     }
   }
 }