add assertion on get charactor info

Runtime/ui/painting/txt/font_manager.cs

 
         public void addFont(Font font) {
             D.assert(font != null);
+            D.assert(font.dynamic, $"adding font which is not dynamic is not allowed {font.name}");
+            FontInfo current;
+            this._fonts.TryGetValue(font.name, out current);
+            D.assert(current == null || current.font == font, $"font with name {font.name} already exists");
-            foreach (var fontName in font.fontNames) {
-                this._fonts[fontName] = fontInfo;
-            }
+            this._fonts[font.name] = fontInfo;
         }
 
         internal FontInfo getOrCreate(string name) {
             osFont.material.mainTexture.hideFlags = HideFlags.DontSave;
 
             var newFont = new FontInfo(osFont);
-            foreach (var fontName in osFont.fontNames) {
-                this._fonts[fontName] = newFont;
-            }
+            this._fonts[osFont.name] = newFont;
 
             return newFont;
         }
                 entry.onTextureRebuilt();
             }
         }
+        
+
+    }
+    
+    public static class FontExtension  
+    {  
+        public static CharacterInfo MustGetCharacterInfo(this Font font, char ch, int fontSize, UnityEngine.FontStyle fontStyle)  
+        {  
+            CharacterInfo info;
+            bool success = font.GetCharacterInfo(ch, out info, fontSize, fontStyle);
+            D.assert(success, $"fail to get character info for character '{ch}' (code{(int)ch}) from font: ${font.name}");
+            return info;
+        }  
     }
 }

Runtime/ui/painting/txt/mesh_generator.cs

                     continue;
                 }
 
-                CharacterInfo charInfo;
-                font.GetCharacterInfo(ch, out charInfo, fontSizeToLoad, style.UnityFontStyle);
-
+                CharacterInfo charInfo = font.MustGetCharacterInfo(ch, fontSizeToLoad, style.UnityFontStyle);
                 var minX = charInfo.minX / this._scale;
                 var maxX = charInfo.maxX / this._scale;
                 var minY = charInfo.minY / this._scale;

Runtime/ui/txt/layout.cs

             for (int i = 0; i < count; i++) {
                 int charIndex = start + i;
                 var ch = text[charIndex];
-                CharacterInfo characterInfo;
-                font.GetCharacterInfo(ch, out characterInfo, style.UnityFontSize, style.UnityFontStyle);
+                CharacterInfo characterInfo = font.MustGetCharacterInfo(ch, style.UnityFontSize, style.UnityFontStyle);
 
                 var rect = Rect.fromLTRB(characterInfo.minX, -characterInfo.maxY, characterInfo.maxX,
                     -characterInfo.minY);

Runtime/ui/txt/linebreaker.cs

-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Linq;
 using UnityEngine;
 
 
             if (this._tabWidth == int.MaxValue) {
                 this._font.RequestCharactersInTexture(" ", this._fontSize);
-                CharacterInfo characterInfo;
-                this._font.GetCharacterInfo(' ', out characterInfo, this._fontSize);
+                CharacterInfo characterInfo = this._font.MustGetCharacterInfo(' ', this._fontSize, UnityEngine.FontStyle.Normal);
                 this._tabWidth = characterInfo.advance * kTabSpaceCount;
             }