Try fixing MSVC 2008 build

Fixes https://github.com/harfbuzz/harfbuzz/issues/1374

src/hb-open-type.hh

@@ -337,8 +337,16 @@ struct UnsizedArrayOf
 {
   HB_NO_CREATE_COPY_ASSIGN_TEMPLATE (UnsizedArrayOf, Type);
 
-  inline const Type& operator [] (unsigned int i) const { return arrayZ[i]; }
-  inline Type& operator [] (unsigned int i) { return arrayZ[i]; }
+  /* Unlikely other places, use "int i" instead of "unsigned int i" for our
+   * indexing operator.  For two reasons:
+   * 1. For UnsizedArrayOf, it's not totally unimaginable to want to look
+   *    at items before the start of current array.
+   * 2. Fixes MSVC 2008 "overloads have similar conversions" issue with the
+   *    built-in operator [] that takes int, in expressions like sizeof(array[0])).
+   *    I suppose I could fix that by replacing 0 with 0u, but like this fix
+   *    more now. */
+  inline const Type& operator [] (int i) const { return arrayZ[i]; }
+  inline Type& operator [] (int i) { return arrayZ[i]; }
 
   template <typename T> inline operator T * (void) { return arrayZ; }
   template <typename T> inline operator const T * (void) const { return arrayZ; }