String: Fix logical error in hex parsing code

modules/juce_core/text/juce_CharacterFunctions.h

@@ -500,10 +500,10 @@ public:
 
             while (! t.isEmpty())
             {
-                auto hexValue = static_cast<ResultType> (CharacterFunctions::getHexDigitValue (t.getAndAdvance()));
+                auto hexValue = CharacterFunctions::getHexDigitValue (t.getAndAdvance());
 
                 if (hexValue >= 0)
-                    result = static_cast<ResultType> (result << 4) | hexValue;
+                    result = static_cast<ResultType> (result << 4) | static_cast<ResultType> (hexValue);
             }
 
             return result;

modules/juce_core/text/juce_String.cpp

@@ -2467,6 +2467,9 @@ public:
             expect (String (StringRef ("abc")) == StringRef ("abc"));
             expect (String ("abc") + StringRef ("def") == "abcdef");
 
+            expect (String ("0x00").getHexValue32() == 0);
+            expect (String ("0x100").getHexValue32() == 256);
+
             String s2 ("123");
             s2 << ((int) 4) << ((short) 5) << "678" << L"9" << '0';
             s2 += "xyz";