uucore: format: Fix capitalization of 0 in scientific formating

0.0E+00 was not capitalized properly when using `%E` format.

Fixes #7382.

Test: cargo test --package uucore --all-features float
Test: cargo run printf "%E\n" 0 => 0.000000E+00

src/uucore/src/lib/features/format/num_format.rs

@@ -350,11 +350,16 @@ fn format_float_scientific(
     case: Case,
     force_decimal: ForceDecimal,
 ) -> String {
+    let exp_char = match case {
+        Case::Lowercase => 'e',
+        Case::Uppercase => 'E',
+    };
+
     if f == 0.0 {
         return if force_decimal == ForceDecimal::Yes && precision == 0 {
-            "0.e+00".into()
+            format!("0.{exp_char}+00")
         } else {
-            format!("{:.*}e+00", precision, 0.0)
+            format!("{:.*}{exp_char}+00", precision, 0.0)
         };
     }
 
@@ -375,11 +380,6 @@ fn format_float_scientific(
         ""
     };
 
-    let exp_char = match case {
-        Case::Lowercase => 'e',
-        Case::Uppercase => 'E',
-    };
-
     format!("{normalized:.precision$}{additional_dot}{exp_char}{exponent:+03}")
 }
 
@@ -582,6 +582,10 @@ mod test {
         assert_eq!(f(12.345_678_9), "1.234568e+01");
         assert_eq!(f(1_000_000.0), "1.000000e+06");
         assert_eq!(f(99_999_999.0), "1.000000e+08");
+
+        let f = |x| format_float_scientific(x, 6, Case::Uppercase, ForceDecimal::No);
+        assert_eq!(f(0.0), "0.000000E+00");
+        assert_eq!(f(123_456.789), "1.234568E+05");
     }
 
     #[test]