Make type conversions explicit. (#7595)

As Java does not support unsigned integer types, the value types
are "rounded up" (an uint32 is represented as a long) but persisted
correctly (an uint32 is persisted as 4 bytes).

This CL makes a cast operation explicit so that the compiler
does not throw warning messages.

Co-authored-by: Dominic Battre <battre@chromium.org>
Co-authored-by: Derek Bailey <derekbailey@google.com>

src/idl_gen_java.cpp

@@ -1893,6 +1893,7 @@ class JavaGenerator : public BaseGenerator {
           }
         } else {
           code += " " + name + " = ";
+          code += SourceCast(field_type);
           code += "_o";
           for (size_t i = 0; i < array_lengths.size(); ++i) {
             code += "." + namer_.Method("get", array_lengths[i].name) + "()";