[core] Keep yOffset in case ascender is not available, preventing breaking existed render tests

Author: zmiao

src/mbgl/text/shaping.cpp

@@ -329,7 +329,6 @@ void shapeLines(Shaping& shaping,
     float y = 0;
     float maxLineLength = 0;
 
-
     const float justify = textJustify == style::TextJustifyType::Right ? 1 :
         textJustify == style::TextJustifyType::Left ? 0 :
         0.5;
@@ -365,15 +364,17 @@ void shapeLines(Shaping& shaping,
             // from the horizontal baseline to the highest ‘character’ coordinate in a font face.
             // Since we're laying out at 24 points, we need also calculate how much it will move
             // when we scale up or down.
-            const double baselineOffset =
-                -glyph.metrics.ascender * section.scale + (lineMaxScale - section.scale) * util::ONE_EM;
+            const bool hasBaseline = glyph.metrics.ascender != 0 && glyph.metrics.descender != 0;
+            const double baselineOffset = (hasBaseline ? (-glyph.metrics.ascender * section.scale) : shaping.yOffset) +
+                                          (lineMaxScale - section.scale) * util::ONE_EM;
 
             if (writingMode == WritingModeType::Horizontal ||
                 // Don't verticalize glyphs that have no upright orientation if vertical placement is disabled.
                 (!allowVerticalPlacement && !util::i18n::hasUprightVerticalOrientation(codePoint)) ||
                 // If vertical placement is ebabled, don't verticalize glyphs that
                 // are from complex text layout script, or whitespaces.
-                (allowVerticalPlacement && (util::i18n::isWhitespace(codePoint) || util::i18n::isCharInComplexShapingScript(codePoint)))) {
+                (allowVerticalPlacement &&
+                 (util::i18n::isWhitespace(codePoint) || util::i18n::isCharInComplexShapingScript(codePoint)))) {
                 shaping.positionedGlyphs.emplace_back(
                     codePoint, x, y + baselineOffset, false, section.fontStackHash, section.scale, sectionIndex);
                 x += glyph.metrics.advance * section.scale + spacing;
@@ -400,7 +401,7 @@ void shapeLines(Shaping& shaping,
 
     align(shaping, justify, anchorAlign.horizontalAlign, anchorAlign.verticalAlign, maxLineLength,
           lineHeight, lines.size());
-    const float height = y - Shaping::yOffset;
+    const float height = y;
     // Calculate the bounding box
     shaping.top += -anchorAlign.verticalAlign * height;
     shaping.bottom = shaping.top + height;