Don't pass nullptr as the 1st arg of from_chars

`from_chars` marks them as `nonnull`, and this is
the case for empty string.

Existing `from_chars` implementation returns
`invalid_argument` which results in `return false`
from `SimpleAtod`.

PiperOrigin-RevId: 820759784
Change-Id: I6635e4eaf339eb178d32f616189f7733808019f5

Author: Abseil Team

absl/strings/numbers.cc

@@ -81,11 +81,15 @@ bool SimpleAtof(absl::string_view str, float* absl_nonnull out) {
 bool SimpleAtod(absl::string_view str, double* absl_nonnull out) {
   *out = 0.0;
   str = StripAsciiWhitespace(str);
+  if (str.empty()) {
+    // absl::from_chars doesn't accept empty strings.
+    return false;
+  }
   // std::from_chars doesn't accept an initial +, but SimpleAtod does, so if one
   // is present, skip it, while avoiding accepting "+-0" as valid.
-  if (!str.empty() && str[0] == '+') {
+  if (str[0] == '+') {
     str.remove_prefix(1);
-    if (!str.empty() && str[0] == '-') {
+    if (str.empty() || str[0] == '-') {
       return false;
     }
   }