fix(math): Properly handle empty final line in TeX-like math tables w…

[Omikhleia]

…ithout losing content

Closes #2303

$$`\table[columnalign=left left]{
  a & 1 \\
  b & 2 \\
}`{numbered=true}

$$`\table[columnalign=left left]{
  a & 1 \\
  b & 2
}`{numbered=true}

$$`\table[columnalign=left left]{
  a & 1 \\
    & 2 }`{numbered=true}

$$`\table[columnalign=left left]{
  a & 1 \\
    & 2 \\}`{numbered=true}