Multiple different pragma versions are not considered and file is randomly taken (probably iterator.next())

[rbrtjhs]

I had a problem when I pulled a project which had different versions of solidity files.

Example:
File1.sol:
pragma solidity >0.5.0 <=0.6.0

File2.sol
pragma solidity >0.5.0 <=0.7.0

Sometimes it will take solidity version from File2.sol, sometimes it will take solidity version from File1.sol.
What is problem?
If it randomly takes files and it takes pragma of File2.sol it will take solc 0.6.12 which will not be able to compile File1.

Here is a test which proves this:
Solidity:
File1.sol:

pragma solidity >=0.5.0 <0.6.0;

contract File1 {

}

File2.sol:

pragma solidity >=0.5.0 <0.7.0;

contract File2 {

}

Java:

@Test
    public void differentPragmas() {
        //delete /home/$user/.web3j folder to download evrerytime (fresh install) new solc version
        String currentUsersHomeDir = System.getProperty("user.home");
        try {
            FileUtils.deleteDirectory(Paths.get(currentUsersHomeDir + "/.web3j").toFile());
        } catch (IOException e) {
            e.printStackTrace();
        }
        List<String> source = new LinkedList<>();
        //it will download 0.6.12 version
        source.add("File2.sol");
        source.add("File1.sol");
        CompilerResult result = solidityCompiler.compileSrc("src/test/resources/issue-70", source, new String[0], SolidityCompiler.Options.ABI, SolidityCompiler.Options.BIN);
        Assert.assertTrue(result.errors.isEmpty());
    }

First commit in the PR #71 has the test which does not work and commit after contains a simple approach to the solution.