tdf#71603: Improve font fallback on Windows a bit

Check all missing characters, not just the first one. Also the calling
sites for GlyphFallbackFontSubstitution hook expect the OUString to be
updated to have only any characters not supported by the returned font.

Change-Id: Ife56d692c05433f2f7fe02db3ef1562181dc3d53

vcl/win/gdi/salfont.cxx

@@ -151,15 +151,15 @@ class WinGlyphFallbackSubstititution
     bool FindFontSubstitute( FontSelectPattern&, OUString& rMissingChars ) const override;
 private:
     HDC mhDC;
-    bool HasMissingChars( PhysicalFontFace*, const OUString& rMissingChars ) const;
+    bool HasMissingChars(PhysicalFontFace*, OUString& rMissingChars) const;
 };
 
 inline WinGlyphFallbackSubstititution::WinGlyphFallbackSubstititution( HDC hDC )
 :   mhDC( hDC )
 {}
 
 // does a font face hold the given missing characters?
-bool WinGlyphFallbackSubstititution::HasMissingChars( PhysicalFontFace* pFace, const OUString& rMissingChars ) const
+bool WinGlyphFallbackSubstititution::HasMissingChars(PhysicalFontFace* pFace, OUString& rMissingChars) const
 {
     WinFontFace* pWinFont = static_cast< WinFontFace* >(pFace);
     FontCharMapRef xFontCharMap = pWinFont->GetFontCharMap();
@@ -194,19 +194,24 @@ bool WinGlyphFallbackSubstititution::HasMissingChars( PhysicalFontFace* pFace, c
         return false;
 
     int nMatchCount = 0;
-    // static const int nMaxMatchCount = 1; // TODO: tolerate more missing characters?
+    std::vector<sal_UCS4> rRemainingCodes;
     const sal_Int32 nStrLen = rMissingChars.getLength();
-    for( sal_Int32 nStrIdx = 0; nStrIdx < nStrLen; /* ++nStrIdx unreachable code, see the 'break' below */ )
+    sal_Int32 nStrIdx = 0;
+    while (nStrIdx < nStrLen)
     {
         const sal_UCS4 uChar = rMissingChars.iterateCodePoints( &nStrIdx );
-        nMatchCount += xFontCharMap->HasChar( uChar ) ? 1 : 0;
-        break; // for now
+        if (xFontCharMap->HasChar(uChar))
+            nMatchCount++;
+        else
+            rRemainingCodes.push_back(uChar);
     }
 
     xFontCharMap = nullptr;
 
-    const bool bHasMatches = (nMatchCount > 0);
-    return bHasMatches;
+    if (nMatchCount > 0)
+        rMissingChars = OUString(rRemainingCodes.data(), rRemainingCodes.size());
+
+    return nMatchCount > 0;
 }
 
 namespace