ImFontConfig: Clarified persistence requirement of GlyphRanges array (#651)

imgui.h

@@ -1254,7 +1254,7 @@ struct ImFontConfig
     int             OversampleH, OversampleV;   // 3, 1     // Rasterize at higher quality for sub-pixel positioning. We don't use sub-pixel positions on the Y axis.
     bool            PixelSnapH;                 // false    // Align every character to pixel boundary (if enabled, set OversampleH/V to 1)
     ImVec2          GlyphExtraSpacing;          // 0, 0     // Extra spacing (in pixels) between glyphs
-    const ImWchar*  GlyphRanges;                //          // List of Unicode range (2 value per range, values are inclusive, zero-terminated list)
+    const ImWchar*  GlyphRanges;                //          // Pointer to a user-provided list of Unicode range (2 value per range, values are inclusive, zero-terminated list). THE ARRAY DATA NEEDS TO PERSIST AS LONG AS THE FONT IS ALIVE.
     bool            MergeMode;                  // false    // Merge into previous ImFont, so you can combine multiple inputs font into one ImFont (e.g. ASCII font + icons + Japanese glyphs).
     bool            MergeGlyphCenterV;          // false    // When merging (multiple ImFontInput for one ImFont), vertically center new glyphs instead of aligning their baseline
 
@@ -1273,6 +1273,7 @@ struct ImFontConfig
 //  3. Upload the pixels data into a texture within your graphics system.
 //  4. Call SetTexID(my_tex_id); and pass the pointer/identifier to your texture. This value will be passed back to you during rendering to identify the texture.
 //  5. Call ClearTexData() to free textures memory on the heap.
+// NB: If you use a 'glyph_ranges' array you need to make sure that your array persist up until the ImFont is cleared. We only copy the pointer, not the data.
 struct ImFontAtlas
 {
     IMGUI_API ImFontAtlas();