ShaderTools,Trade: no longer say we return an empty Array on error.

Forgot to update the docs in 51f7862e00.

src/Magnum/ShaderTools/AbstractConverter.h

@@ -336,11 +336,10 @@ converter plugins.
 As each converter has different requirements on the source, its format and
 options set, you're expected to perform error handling on the application side
 --- if a conversion or linking fails, you get an empty
-@relativeref{Corrade,Containers::Optional} /
+@relativeref{Corrade,Containers::Optional} or @cpp false @ce and a reason
-@relativeref{Corrade,Containers::Array} or @cpp false @ce and a reason printed
+printed to @relativeref{Magnum,Error}. Everything else (using a feature not
-to the error output. Everything else (using a feature not implemented in the
+implemented in the converter, ...) is treated as a programmer error and will
-converter, ...) is treated as a programmer error and will produce the usual
+produce the usual assertions.
-assertions.
 
 @m_class{m-note m-success}
 

src/Magnum/Trade/AbstractImageConverter.h

@@ -492,11 +492,10 @@ what the particular converter supports, @ref convertToFile(),
 As each converter has different requirements and supports different pixel
 formats, you're expected to perform error handling on the application side ---
 if a conversion fails, you get an empty
-@relativeref{Corrade,Containers::Optional} /
+@relativeref{Corrade,Containers::Optional} or @cpp false @ce and a reason
-@relativeref{Corrade,Containers::Array} or @cpp false @ce and a reason printed
+printed to @relativeref{Magnum,Error}. Everything else (using a feature not
-to the error output. Everything else (using a feature not implemented in the
+implemented in the converter, ...) is treated as a programmer error and will
-converter, ...) is treated as a programmer error and will produce the usual
+produce the usual assertions.
-assertions.
 
 @subsection Trade-AbstractImageConverter-usage-file Saving an image to a file
 

src/Magnum/Trade/AbstractSceneConverter.h

@@ -192,11 +192,10 @@ what the particular converter supports, @ref convertToFile(),
 As each converter has different requirements on the input data layout and
 vertex formats, you're expected to perform error handling on the application
 side --- if a conversion fails, you get an empty
-@relativeref{Corrade,Containers::Optional} /
+@relativeref{Corrade,Containers::Optional} or @cpp false @ce and a reason
-@relativeref{Corrade,Containers::Array} or @cpp false @ce and a reason printed
+printed to @relativeref{Magnum,Error}. Everything else (using a feature not
-to the error output. Everything else (using a feature not implemented in the
+implemented in the converter, ...) is treated as a programmer error and will
-converter, ...) is treated as a programmer error and will produce the usual
+produce the usual assertions.
-assertions.
 
 @subsection Trade-AbstractSceneConverter-usage-file Saving a mesh to a file