LibWeb: Remove early continue in size parsing

Step 5 of parsing was always skipped because step 4 continues.

Running step 5 causes some of the denominators to be 0 and causes
divide by zero error in CSSPixelFraction.

SVG Image with height of 0 will cause divide by zero error when
calculating intrinsic aspect ratio of SVGDecoderImageData.

We also get a divide by zero error in AlignContent::SpaceBetween of the
FlexFormatingContext.

During auto track stretching in GridFormatingContext there is a
possibility for count_of_auto_max_sizing_tracks to stay 0.

Userland/Libraries/LibWeb/PixelUnits.h

@@ -294,6 +294,7 @@ public:
         : m_numerator(numerator)
         , m_denominator(denominator)
     {
+        VERIFY(denominator != 0);
     }
 
     explicit constexpr CSSPixelFraction(CSSPixels value)
@@ -307,6 +308,7 @@ public:
         : m_numerator(numerator)
         , m_denominator(denominator)
     {
+        VERIFY(denominator != 0);
     }
 
     constexpr operator CSSPixels() const