[librsvg] Appease "make distcheck" by adding an empty source list for librsvg_c_api_la_SOURCES

[Federico Mena Quintero <federico src gnome org>]

commit 601b2f0ef2185b6f4ad776084e131eae1423e0cf
Author: Federico Mena Quintero <federico gnome org>
Date:   Mon Aug 26 17:04:12 2019 +0300

    Appease "make distcheck" by adding an empty source list for librsvg_c_api_la_SOURCES
    
    Otherwise it thinks we would have a single librsvg_c_api.c source file.

 Makefile.am | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/Makefile.am b/Makefile.am
index 91867189..7704d197 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,6 +5,11 @@ NULL =
 lib_LTLIBRARIES = librsvg-@RSVG_API_MAJOR_VERSION@.la
 noinst_LTLIBRARIES = librsvg_c_api.la
 
+# This is empty, because automake wants to have a C sources list for
+# the LTLIBRARIES.  See LIBRSVG_INTERNALS_SRC below for the real list
+# of Rust sources.
+librsvg_c_api_la_SOURCES =
+
 bin_PROGRAMS = rsvg-convert
 
 include rsvg-c-srcs.mk
@@ -13,7 +18,7 @@ librsvg_@RSVG_API_MAJOR_VERSION@_la_SOURCES = \
        $(librsvg_c_srcs)                       \
        $(NULL)
 
-LIBRSVG_INTERNALS_SRC =                                        \
+LIBRSVG_INTERNALS_SRC =                                                \
        Cargo.toml                                              \
        rsvg_internals/Cargo.toml                               \
        rsvg_internals/build.rs                                 \