use ASCII blank even for graphical meter in UTF-8 mode

If the terminal has no font with braille characters we see... Nothing
useful. Use an ASCII blank at least, so we have an idea about what's
going on.

Meter.c

@@ -312,7 +312,7 @@ static void BarMeterMode_draw(Meter* this, int x, int y, int w) {
 
 #define PIXPERROW_UTF8 4
 static const char* GraphMeterMode_dotsUtf8[] = {
-   /*00*/"⠀", /*01*/"⢀", /*02*/"⢠", /*03*/"⢰", /*04*/ "⢸",
+   /*00*/" ", /*01*/"⢀", /*02*/"⢠", /*03*/"⢰", /*04*/ "⢸",
    /*10*/"⡀", /*11*/"⣀", /*12*/"⣠", /*13*/"⣰", /*14*/ "⣸",
    /*20*/"⡄", /*21*/"⣄", /*22*/"⣤", /*23*/"⣴", /*24*/ "⣼",
    /*30*/"⡆", /*31*/"⣆", /*32*/"⣦", /*33*/"⣶", /*34*/ "⣾",