Fix a build error

Author: tannergooding

src/libraries/System.Private.CoreLib/src/System/Number.Dragon4.cs

@@ -154,6 +154,10 @@ private static uint Dragon4(ulong mantissa, int exponent, uint mantissaHighBitId
                     // scaledMarginLow = 2 * 2^(-1)
                     BigInteger.SetUInt32(out scaledMarginLow, 1);
                 }
+
+                // This is unused for this path, but we need it viewed as "initialized" so the
+                // scaledMarginHigh tracking works as expected.
+                Unsafe.SkipInit(out optionalMarginHigh);
             }
 
             scoped ref BigInteger scaledMarginHigh = ref (hasUnequalMargins ? ref optionalMarginHigh : ref scaledMarginLow);

src/libraries/System.Private.CoreLib/src/System/Number.Formatting.cs

@@ -418,9 +418,11 @@ private static int GetFloatingPointMaxDigitsAndPrecision(char fmt, ref int preci
             // We want to fast path the common case of no format and general format + precision.
             // These are commonly encountered and the full switch is otherwise large enough to show up in hot path profiles
 
-            fmt |= 0x20;
+            // Bitwise-or with space (' ') converts null ('\0') to space, any uppercase character to lowercase
+            // and other unsupported characters to something else unsupported.
+            fmt |= ' ';
 
-            if ((fmt == 0x20) || (fmt == 'g'))
+            if ((fmt == ' ') || (fmt == 'g'))
             {
                 // The general format uses the precision specifier to indicate the number of significant
                 // digits to format. This defaults to the shortest roundtrippable string. Additionally,