Fix getindex in a bunch of libgit2

Now actually `throw(BoundsError)` when we should, and don't just
fail silently if something bad happens.

base/libgit2/diff.jl

@@ -36,9 +36,12 @@ function Base.count(diff::GitDiff)
 end
 
 function Base.getindex(diff::GitDiff, i::Csize_t)
+    if i < 1 || i >= count(diff)
+        throw(BoundsError())
+    end
     delta_ptr = ccall((:git_diff_get_delta, :libgit2), Ptr{Void},
                        (Ptr{Void}, Csize_t), diff.ptr, i-1)
-    delta_ptr == C_NULL && return nothing
+    delta_ptr == C_NULL && throw(Error.GitError(Error.ERROR))
     return unsafe_load(convert(Ptr{DiffDelta}, delta_ptr), 1)
 end
 Base.getindex(diff::GitDiff, i::Int) = getindex(diff, Csize_t(i))

base/libgit2/index.jl

@@ -112,9 +112,12 @@ function Base.count(idx::GitIndex)
 end
 
 function Base.getindex(idx::GitIndex, i::Csize_t)
+    if i < 1 || i >= count(idx)
+        throw(BoundsError())
+    end
     ie_ptr = ccall((:git_index_get_byindex, :libgit2), Ptr{Void},
                   (Ptr{Void}, Csize_t), idx.ptr, i-1)
-    ie_ptr == C_NULL && return nothing
+    ie_ptr == C_NULL && throw(Error.GitError(Error.ERROR))
     return unsafe_load(convert(Ptr{IndexEntry}, ie_ptr), 1)
 end
 Base.getindex(idx::GitIndex, i::Int) = getindex(idx, Csize_t(i))

base/libgit2/rebase.jl

@@ -21,9 +21,12 @@ function current(rb::GitRebase)
 end
 
 function Base.getindex(rb::GitRebase, i::Csize_t)
+    if i < 1 || i >= count(rb)
+        throw(BoundsError())
+    end
     rb_op_ptr = ccall((:git_rebase_operation_byindex, :libgit2), Ptr{Void},
                        (Ptr{Void}, Csize_t), rb.ptr, i-1)
-    rb_op_ptr == C_NULL && return nothing
+    rb_op_ptr == C_NULL && throw(Error.GitError(Error.ERROR))
     return unsafe_load(convert(Ptr{RebaseOperation}, rb_op_ptr), 1)
 end
 Base.getindex(rb::GitRebase, i::Int) = getindex(rb, Csize_t(i))

base/libgit2/tree.jl

@@ -18,8 +18,8 @@ end
 
 function filename(te::GitTreeEntry)
     str = ccall((:git_tree_entry_name, :libgit2), Cstring, (Ptr{Void},), te.ptr)
-    str != C_NULL && return unsafe_string(str)
-    return nothing
+    str == C_NULL && throw(Error.GitError(Error.ERROR))
+    return unsafe_string(str)
 end
 
 function filemode(te::GitTreeEntry)

base/libgit2/walker.jl

@@ -50,8 +50,8 @@ end
 
 function repository(w::GitRevWalker)
     ptr = ccall((:git_revwalk_repository, :libgit2), Ptr{Void}, (Ptr{Void},), w.ptr)
-    ptr != C_NULL && return GitRepo(ptr)
-    return  nothing
+    ptr == C_NULL && throw(Error.GitError(Error.ERROR))
+    return GitRepo(ptr)
 end
 
 function Base.map(f::Function, walker::GitRevWalker;