Pass caption value into ImageMagick 7 API in Image#polaroid
In ImageMagick 6, `PolaroidImage()` retrives caption value in inside.
```c
value=GetImageProperty(image,"Caption");
```
@@ -10889,7 +10889,7 @@ Image_polaroid(int argc, VALUE *argv, VALUE self)
Draw *draw;
ExceptionInfo *exception;
#if defined(IMAGEMAGICK_7)
- char *caption = (char *) NULL;
+ const char *caption;
#endif
image = rm_check_destroyed(self);
@@ -10914,6 +10914,7 @@ Image_polaroid(int argc, VALUE *argv, VALUE self)
exception = AcquireExceptionInfo();
#if defined(IMAGEMAGICK_7)
+ caption = GetImageProperty(clone, "Caption", exception);
new_image = PolaroidImage(clone, draw->info, caption, angle, image->interpolate, exception);
#else
new_image = PolaroidImage(clone, draw->info, angle, exception);
