eina_mono: re-throw exception to preserve stack details

Summary:
fix CA2200
ref T8426

Test Plan:
meson setup -Dbindings=mono,cxx -Dmono-beta=true
ninja test

Reviewers: lauromoura, felipealmeida, brunobelo

Reviewed By: lauromoura

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Maniphest Tasks: T8426

Differential Revision: https://phab.enlightenment.org/D10462

src/bindings/mono/eina_mono/eina_common.cs

@@ -205,10 +205,10 @@ public static class StringConversion
             Marshal.WriteByte(native + strbuf.Length, 0); // write the terminating null
             return native;
         }
-        catch(Exception e)
+        catch(Exception)
         {
             MemoryNative.Free(native);
-            throw e;
+            throw;
         }
     }