make conversions explicit

Found with MSVC's C4244

Signed-off-by: Rosen Penev <rosenp@gmail.com>

app/exiv2.cpp

@@ -469,7 +469,7 @@ int Params::option(int opt, const std::string& optArg, int optOpt) {
 
 int Params::setLogLevel(const std::string& optArg) {
   int rc = 0;
-  const char logLevel = tolower(optArg[0]);
+  const auto logLevel = static_cast<char>(tolower(optArg[0]));
   switch (logLevel) {
     case 'd':
       Exiv2::LogMsg::setLevel(Exiv2::LogMsg::debug);

src/futils.cpp

@@ -81,7 +81,7 @@ char to_hex(char code) {
 
 /// @brief Convert a hex character to its integer value.
 char from_hex(char ch) {
-  return isdigit(ch) ? ch - '0' : tolower(ch) - 'a' + 10;
+  return isdigit(ch) ? ch - '0' : static_cast<char>(tolower(ch)) - 'a' + 10;
 }
 
 std::string urlencode(const std::string& str) {

src/image.cpp

@@ -469,9 +469,9 @@ void Image::printIFDStructure(BasicIo& io, std::ostream& out, Exiv2::PrintStruct
           if (bNikon) {
             // tag is an embedded tiff
             const long byteslen = count - jump;
-            DataBuf bytes(byteslen);                                                  // allocate a buffer
-            io.readOrThrow(bytes.data(), byteslen, ErrorCode::kerCorruptedMetadata);  // read
-            MemIo memIo(bytes.c_data(), byteslen);                                    // create a file
+            auto b = DataBuf(byteslen);                                           // allocate a buffer
+            io.readOrThrow(b.data(), byteslen, ErrorCode::kerCorruptedMetadata);  // read
+            MemIo memIo(b.c_data(), byteslen);                                    // create a file
             printTiffStructure(memIo, out, option, depth + 1);
           } else {
             // tag is an IFD

src/sonymn_int.cpp

@@ -2289,7 +2289,7 @@ static DataBuf sonyTagCipher(uint16_t /* tag */, const byte* bytes, size_t size,
   byte code[256];
   for (uint32_t i = 0; i < 249; i++) {
     if (bDecipher) {
-      code[(i * i * i) % 249] = i;
+      code[(i * i * i) % 249] = static_cast<byte>(i);
     } else {
       code[i] = (i * i * i) % 249;
     }

src/version.cpp

@@ -127,8 +127,7 @@ static std::vector<std::string> getLoadedLibraries() {
     char szFilename[_MAX_PATH];
     for (DWORD h = 0; h < cbNeeded / sizeof(handles[0]); h++) {
       GetModuleFileNameA(handles[h], szFilename, static_cast<DWORD>(std::size(szFilename)));
-      std::string path(szFilename);
-      pushPath(path, libs, paths);
+      pushPath(szFilename, libs, paths);
     }
   }
 #elif defined(__APPLE__)