Fix parsing error if ssa style contains leading or trailing whitespaces

[bytedream]

[Script Info]

[V4+ Styles]
Format: Name,Fontname,Fontsize,PrimaryColour,SecondaryColour,OutlineColour,BackColour,Bold,Italic,Underline,StrikeOut,ScaleX,ScaleY,Spacing,Angle,BorderStyle,Outline,Shadow,Alignment,MarginL,MarginR,MarginV,Encoding
Style: Default,Arial, 25.5,&H00FFFFFF,&H00000000,&H00000000,&H00000000,-1 ,0,0,0,120,120,0,0,1,1,1,2,0000,0000,0030,0"

Previously this would fail parsing the fontsize because it has an leading whitespace (only an example, any number with leading whitespace would fail)