Clang: Fix SourceLocation column recalculation

Fix column conversion according to the fact that
columns are 1-based.

Change-Id: I75e9b966d96b9bb7648822b564e57f8838ebb3f8
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/tools/clangbackend/source/sourcelocation.cpp

@@ -102,7 +102,7 @@ SourceLocation::SourceLocation(CXTranslationUnit cxTranslationUnit,
         // (2) column in Clang is the utf8 byte offset from the beginning of the line.
         // Here we convert column from (2) to (1).
         column_ = static_cast<uint>(QString::fromUtf8(&contents[lineStart],
-                                                      static_cast<int>(column_)).size());
+                                                      static_cast<int>(column_) - 1).size()) + 1;
     }
 }