Fix precision parsing in string_format

The 4th group in the regular expression matches `(\.\d+)?` so the dot
should be ignored before the string can be parsed to an int.

Author: romainbrenguier

Diff for: src/solvers/strings/string_constraint_generator_format.cpp

@@ -198,7 +198,7 @@ static format_specifiert format_specifier_of_match(std::smatch &m)
   int index = m[1].str().empty() ? -1 : std::stoi(m[1].str());
   std::string flag = m[2].str();
   int width = m[3].str().empty() ? -1 : std::stoi(m[3].str());
-  int precision = m[4].str().empty() ? -1 : std::stoi(m[4].str());
+  int precision = m[4].str().empty() ? -1 : std::stoi(m[4].str().substr(1));
   std::string tT = m[5].str();
 
   bool dt = !tT.empty();