Fix some unreachable code and possible loss of data warnings

Author: stefanuhrig

src/odbc/Config.h

@@ -23,7 +23,15 @@
 #    endif
 #endif
 //------------------------------------------------------------------------------
-#ifdef _WIN32
+#if defined(__clang__) || defined(__GNUC__)
+#    define ODBC_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#    define ODBC_UNREACHABLE __assume(false)
+#else
+#    define ODBC_UNREACHABLE ((void)0)
+#endif
+//------------------------------------------------------------------------------
+#ifdef _MSC_VER
 #   pragma warning(disable: 4251 4275)
 #endif
 //------------------------------------------------------------------------------

src/odbc/StringConverter.cpp

@@ -53,7 +53,7 @@ u16string StringConverter::utf8ToUtf16(const char* begin, const char* end)
         }
         else
         {
-            str.push_back(cp.second);
+            str.push_back(static_cast<char16_t>(cp.second));
         }
     }
 

src/odbc/internal/charset/Utf8.h

@@ -52,7 +52,7 @@ inline bool isValidSequence(int len, const char* c)
         return ((c[0] & 0xF8) == 0xF0) && ((c[1] & 0xC0) == 0x80)
                && ((c[2] & 0xC0) == 0x80) && ((c[3] & 0xC0) == 0x80);
     }
-    assert(false);
+    ODBC_UNREACHABLE;
 }
 //------------------------------------------------------------------------------
 /**
@@ -121,7 +121,7 @@ inline char32_t decode(int len, const char* c)
     case 4:
         return decode4(c);
     }
-    assert(false);
+    ODBC_UNREACHABLE;
 }
 //------------------------------------------------------------------------------
 } // namespace utf8