Clear errno before calling strtod()

Fixes GH-27.

src/load.c

@@ -525,6 +525,7 @@ static int lex_scan_number(lex_t *lex, int c, json_error_t *error)
     lex_unget_unsave(lex, c);
 
     saved_text = strbuffer_value(&lex->saved_text);
+    errno = 0;
     value = strtod(saved_text, &end);
     assert(end == saved_text + lex->saved_text.length);