Use assign for deserialize instead of temporary std::string (#241)

Signed-off-by: Samuel Hyyppä <[email protected]>
Co-authored-by: Samuel Hyyppä <[email protected]>

Author: SamuelH91

include/fastcdr/Cdr.h

@@ -1793,7 +1793,7 @@ class Cdr
     {
         uint32_t length = 0;
         const char* str = read_string(length);
-        value = std::string(str, length);
+        value.assign(str, length);
         return *this;
     }
 

include/fastcdr/FastCdr.h

@@ -1552,7 +1552,7 @@ class Cdr_DllAPI FastCdr
     {
         uint32_t length = 0;
         const char* str = read_string(length);
-        string_t = std::string(str, length);
+        string_t.assign(str, length);
         return *this;
     }