strconv: minor cleanup in f64_to_str_lnd1() (#13804)

vlib/strconv/format_mem.c.v

@@ -158,31 +158,38 @@ pub fn f64_to_str_lnd1(f f64, dec_digit int) string {
 
 		// get sign and decimal parts
 		for c in s {
-			if c == `-` {
+			match c {
+				`-` {
 					sgn = -1
 					i++
-			} else if c == `+` {
+				}
+				`+` {
 					sgn = 1
 					i++
-			} else if c >= `0` && c <= `9` {
+				}
+				`0`...`9` {
 					b[i1] = c
 					i1++
 					i++
-			} else if c == `.` {
+				}
+				`.` {
 					if sgn > 0 {
 						d_pos = i
 					} else {
 						d_pos = i - 1
 					}
 					i++
-			} else if c == `e` {
+				}
+				`e` {
 					i++
 					break
-			} else {
+				}
+				else {
 					s.free()
 					return '[Float conversion error!!]'
 				}
 			}
+		}
 		b[i1] = 0
 
 		// get exponent